9

The Causes of
Great Power War

Security competition is endemic to daily life in the international system, but war is not. Only occasionally does security competition give way to war. This chapter will offer a structural theory that accounts for that deadly shift. In effect, I seek to explain the causes of great-power war, defined as any conflict involving at least one great power.

One might surmise that international anarchy is the key structural factor that causes states to fight wars. After all, the best way for states to survive in an anarchic system in which other states have some offensive capability and intentions that might be hostile is to have more rather than less power. This logic, explained in Chapter 2, drives states to strive to maximize their share of world power, which sometimes means going to war against a rival state. There is no question that anarchy is a deep cause of war. G. Lowes Dickinson put this point well in his account of what caused World War I: “Some one state at any moment may be the immediate offender; but the main and permanent offence is common to all states. It is the anarchy which they are all responsible for perpetuating.”¹

Anarchy alone, however, cannot account for why security competition sometimes leads to war but sometimes does not. The problem is that anarchy is a constant—the system is always anarchic—whereas war is not. To account for this important variation in state behavior, it is necessary to consider another structural variable: the distribution of power among the leading states in the system. As discussed in Chapter 8, power in the international system is usually arranged in three different ways: bipolarity, balanced multipolarity, and unbalanced multipolarity. Thus, to explore the effect of the distribution of power on the likelihood of war, we need to know whether the system is bipolar or multipolar, and if it is multipolar, whether or not there is a potential hegemon among the great powers. The core of my argument is that bipolar systems tend to be the most peaceful, and unbalanced multipolar systems are the most prone to deadly conflict. Balanced multipolar sytems fall somewhere in between.

Structural theories such as offensive realism are at best crude predictors of when security competition leads to war. They are not capable of explaining precisely how often war will occur in one kind of system compared to another. Nor are they capable of predicting exactly when wars will occur. For example, according to offensive realism, the emergence of Germany as a potential hegemon in the early 1900s made it likely that there would be a war involving all the European great powers. But the theory cannot explain why war occured in 1914 rather than 1912 or 1916.²

These limitations stem from the fact that nonstructural factors sometimes play an important role in determining whether or not a state goes to war. States usually do not fight wars for security reasons alone. As noted in Chapter 2, for instance, although Otto von Bismarck was driven in good part by realist calculations when he took Prussia to war three times between 1864 and 1870, each of his decisions for war was also influenced by nationalism and other domestic political calculations. And yet structural forces do exert a powerful influence on state behavior. It can be no other way if states care deeply about their survival. Thus, focusing exclusively on structure should tell us a lot about the origins of great-power war.

Many theories about the causes of war have been propounded, which is not surprising, since the subject has always been of central importance to students of international politics. Some of those theories treat human nature as the taproot of conflict, while others focus on individual leaders, domestic politics, political ideology, capitalism, economic interdependence, and the structure of the international system.³ In fact, a handful of prominent theories point to the distribution of power as the key to understanding international conflict. For example, Kenneth Waltz maintains that bipolarity is less prone to war than multipolarity, whereas Karl Deutsch and J. David Singer argue the opposite.⁴ Other scholars focus not on the polarity of the system, but on whether there is a preponderant power in the system. Classical realists such as Hans Morgenthau argue that peace is most likely when there is no dominant power, but instead a rough balance of power among the leading states. In contrast, Robert Gilpin and A.F.K. Organski argue that the presence of a preponderant power fosters stability.⁵

Offensive realism, which takes into account polarity as well as the balance of power among the leading states in the system, agrees that bipolarity is more stable than multipolarity but goes beyond that assertion by distinguishing between multipolar systems with or without a potential hegemon. This distinction between balanced and unbalanced multipolar systems, I argue, is important for understanding the history of great-power war. Offensive realism also agrees with the classical realists’ claim that peace is more likely if there is no preponderant power in the system, but it goes beyond that perspective by emphasizing that stability also depends on whether the system is bipolar or multipolar.

Showing how offensive realism explains great-power war involves a two-step process. In the next three sections, I spell out my theory and show that the causal logic underpinning it is sound and compelling. In the subsequent two sections, the theory is tested to see how well it explains both the outbreak of great-power war and the periods of relative peace in Europe between 1792 and 1990. Specifically, I look to see how much great-power war there was during the periods when Europe was characterized by bipolarity, by balanced multipolarity, and by unbalanced multipolarity. Finally, my brief conclusion discusses how the presence of nuclear weapons during the Cold War affects the analysis.

STRUCTURE AND WAR

The main causes of war are located in the architecture of the international system. What matters most is the number of great powers and how much power each controls. A system can be either bipolar or multipolar, and power can be distributed more or less evenly among the leading states. The power ratios among all the great powers affect the prospects for stability, but the key ratio is that between the two most formidable states in the system. If there is a lopsided power gap, the number one state is a potential hegemon.⁶ A system that contains an aspiring hegemon is said to be unbalanced; a system without such a dominant state is said to be balanced. Power need not be distributed equally among all the major states in a balanced system, although it can be. The basic requirement for balance is that there not be a marked difference in power between the two leading states. If there is, the system is unbalanced.

Combining these two dimensions of power produces four possible kinds of sytems: 1) unbalanced bipolarity, 2) balanced bipolarity, 3) unbalanced multipolarity, and 4) balanced multipolarity. Unbalanced bipolarity is not a useful category, because this kind of system is unlikely to be found in the real world. I know of none in modern times. It is certainly possible that some region might find itself with just two great powers, one of which is markedly more powerful than the other. But that system is likely to disappear quickly, because the stronger state is likely to conquer its weaker rival, who would have no other great power to turn to for help, since by definition there are no other great powers. In fact, the weaker power might even capitulate without a fight, making the more powerful state a regional hegemon. In short, unbalanced bipolar systems are so unstable that they cannot last for any appreciable period of time.

Thus we are likely to find power apportioned among the leading states in three different patterns. Bipolar systems (this is shorthand for balanced bipolarity) are ruled by two great powers that have roughly equal strength—or at least neither state is decidedly more powerful than the other. Unbalanced multipolar sytems are dominated by three or more great powers, one of which is a potential hegemon. Balanced multipolar systems are dominated by three or more great powers, none of which is an aspiring hegemon: there is no significant gap in military strength between the system’s leading two states, although some power asymmetries are likely to exist among the great powers.

How do these different distributions of power affect the prospects for war and peace? Bipolar systems are the most stable of the three systems. Great-power wars are infrequent, and when they occur, they are likely to involve one of the great powers fighting against a minor power, not the rival great power. Unbalanced multipolar systems feature the most dangerous distribution of power, mainly because potential hegemons are likely to get into wars with all of the other great powers in the system. These wars invariably turn out to be long and enormously costly. Balanced multipolar sytems occupy a middle ground: great-power war is more likely than in bipolarity, but decidedly less likely than in unbalanced multipolarity. Moreover, the wars between the great powers are likely to be one-on-one or two-on-one engagements, not systemwide conflicts like those that occur when there is a potential hegemon.

Let us now consider why bipolar systems are more stable than multipolar systems, regardless of whether there is a potential hegemon in the mix. Later I will explain why balanced multipolar systems are more stable than unbalanced ones.

BIPOLARITY VS. MULTIPOLARITY

War is more likely in multipolarity than bipolarity for three reasons.⁷ First, there are more opportunities for war, because there are more potential conflict dyads in a multipolar system. Second, imbalances of power are more commonplace in a multipolar world, and thus great powers are more likely to have the capability to win a war, making deterrence more difficult and war more likely. Third, the potential for miscalculation is greater in multipolarity: states might think they have the capability to coerce or conquer another state when, in fact, they do not.

Opportunities for War

A multipolar system has more potential conflict situations than does a bipolar order. Consider great-great power dyads. Under bipolarity, there are only two great powers and therefore only one conflict dyad directly involving them. For example, the Soviet Union was the only great power that the United States could have fought during the Cold War. In contrast, a multipolar system with three great powers has three dyads across which war might break out between the great powers: A can fight B, A can fight C, and B can fight C. A system with five great powers has ten great-great power dyads.

Conflict could also erupt across dyads involving major and minor powers. In setting up a hypothetical scenario, it seems reasonable to assume the same number of minor powers in both the bipolar and multipolar systems, since the number of major powers should have no meaningful effect on the number of minor powers. Therefore, because there are more great powers in multipolarity, there are more great-minor power dyads. Consider the following examples: in a bipolar world with 10 minor powers, there are 20 great-minor power dyads; in a multipolar system with 5 great powers and the same 10 minor powers, there are 50 such dyads.

This disparity in the number of great-minor power dyads in the two systems probably should be tilted further in favor of bipolarity, because it is generally less flexible than multipolarity. Bipolar systems are likely to be rigid structures. Two great powers dominate, and the logic of security competition suggests that they will be unambiguous rivals. Most minor powers find it difficult to remain unattached to one of the major powers in bipolarity, because the major powers demand allegiance from the smaller states. This tightness is especially true in core geographical areas, less so in peripheral areas. The pulling of minor powers into the orbit of one or the other great power makes it difficult for either great power to pick a fight with minor powers closely allied with its adversary; as a result, the numbers of potential conflict situations is substantially less. During the Cold War, for example, the United States was not about to use military force against Hungary or Poland, which were allied with the Soviet Union. Thus, there should probably be substantially fewer than 20 great-minor power dyads in our hypothetical bipolar world.

In contrast, multipolar systems are less firmly structured. The exact form multipolarity takes can vary widely, depending on the number of major and minor powers in the system and the geographical arrangement of those states. Nevertheless, both major and minor powers usually have considerable flexibility regarding alliance partners, and minor powers are less likely to be closely tied to a great power than in a bipolar system. This autonomy, however, leaves minor powers vulnerable to attack from the great powers. Thus, the 50 great-minor power dyads in our hypothetical multipolar system is probably a reasonable number.

Wars between minor powers are largely ignored in this study because the aim is to develop a theory of great-power war. Yet minor-power wars sometimes widen and great powers get dragged into the fighting. Although the subject of escalation lies outside the scope of this study, a brief word is in order about how polarity affects the likelihood of great powers’ getting pulled into wars between minor powers. Basically, that possibility is greater in multipolarity than in bipolarity, because there are more opportunities for minor powers to fight each other in multipolarity, and thus more opportunities for great-power involvement.

Consider that our hypothetical bipolar and multipolar worlds both contain 10 minor powers, which means that there are 45 potential minor-minor power dyads in each system. That number should be markedly reduced for bipolarity, because the general tightness of bipolar sytems makes it difficult for minor powers to go to war against each other. Specifically, both great powers would seek to prevent fighting between their own minor-power allies, as well as conflicts involving minor powers from the rival camps, for fear of escalation. Minor powers have much more room to maneuver in a multipolar system, and thus they have more freedom to fight each other. Greece and Turkey, for example, fought a war between 1921 and 1924, when Europe was multipolar. But they were in no position to fight with each other during the Cold War, when Europe was bipolar, because the United States would not have tolerated a war between any of its European allies, for fear it would have weakened NATO vis-à-vis the Soviet Union.

Imbalances of Power

Power asymmetries among the great powers are more commonplace in multipolarity than bipolarity, and the strong become hard to deter when power is unbalanced, because they have increased capability to win wars.⁸ But even if we assume that the military strength of the great powers is roughly equal, power imbalances that lead to conflict are still more likely in multipolarity than in bipolarity.

Multipolar systems tend toward inequality, whereas bipolar systems tend toward equality, for one principal reason. The more great powers there are in a system, the more likely it is that wealth and population size, the building blocks of military power, will be distributed unevenly among them. To illustrate, let us assume that we live in a world where, regardless of how many great powers populate the system, there is a 50 percent chance that any two great powers will have roughly the same amount of latent power. If there are only two great powers in that world (bipolarity), obviously there is a 50 percent chance that each state will control the same quantity of latent power. But if there are three great powers in that world (multipolarity), there is only a 12.5 percent chance that all of them will have the same amount of latent power. With four great powers (multipolarity), there is less than a 2 percent chance that the ingredients of military might will be distributed evenly among all of them.

One could use a different number for the likelihood that any two states will have equal amounts of latent power—say, 25 percent or 60 percent instead of 50 percent—but the basic story would remain the same. Asymmetries in latent power are more likely to be found among the great powers in multipolarity than in bipolarity, and the more great powers there are in multipolarity, the more remote the chances of symmetry. This is not to say that it is impossible to have a multipolar system in which the great powers possess equal proportions of latent power, but only that it is considerably less likely than in a bipolar system. Of course, the reason for this concern with latent power is that significant variations in wealth and population size among the leading states are likely to lead to disparities in actual military power, simply because some states will be better endowed to pursue an arms race than are others.⁹

But even if we assume that all the major states are equally powerful, imbalances in power still occur more often in multipolarity than in bipolarity. Two great powers in a multipolar system, for example, can join together to attack a third great power, as the United Kingdom and France did against Russia in the Crimean War (1853–56), and Italy and Prussia did against Austria in 1866. This kind of ganging up is impossible in bipolarity, since only two great powers compete. Two great powers can also join forces to conquer a minor power, as Austria and Prussia did against Denmark in 1864, and Germany and the Soviet Union did against Poland in 1939. Ganging up of this sort is logically possible in a bipolar world, but it is highly unlikely because the two great powers are almost certain to be archrivals disinclined to go to war as allies. Furthermore, a major power might use its superior strength to coerce or conquer a minor power. This kind of behavior is more likely in multipolarity than in bipolarity, because there are more potential great-minor power dyads in a multipolar system.

One might argue that balance-of-power dynamics can operate to counter any power imbalances that arise in multipolarity. No state can dominate another if the other states coalesce firmly against it.¹⁰ Indeed, this might be seen as an advantage that multipolarity has over bipolarity, since great-power balancing coalitions are not feasible in a world with only two great powers. But threatened states rarely form effective balancing coalitions in time to contain an aggressor. As Chapter 8 demonstrated, threatened states prefer buck-passing to balancing, but buck-passing directly undermines efforts to build powerful balancing coalitions.

But even when threatened states do balance together in multipolarity, diplomacy is an uncertain process. It can take time to build a defensive coalition, especially if the number of states required to form a balancing alliance is large. An aggressor may conclude that it can gain its objectives before the opposing coalition is fully formed. Finally, geography sometimes prevents balancing states from putting meaningful pressure on aggressors. For example, a major power may not be able to put effective military pressure on a state threatening to cause trouble because they are separated from each other by a large body of water or another state.¹¹

The Potential for Miscalculation

A final problem with multipolarity lies in its tendency to foster miscalculation. Multipolarity leads states to underestimate the resolve of rival states and the strength of opposing coalitions. States then mistakenly conclude that they have the military capability to coerce an opponent, or if that fails, to defeat it in battle.

War is more likely when a state underestimates the willingness of an opposing state to stand firm on issues of difference. It then may push the other state too far, expecting the other to concede when in fact it will choose to fight. Such miscalculation is more likely under multipolarity because the shape of the international order tends to remain fluid, due to the tendency of coalitions to shift. As a result, the nature of the agreed international rules of the road—norms of state behavior, and agreed divisions of territorial rights and other privileges—tend to change constantly. No sooner may the rules of a given adversarial relationship be worked out than that relationship becomes a friendship, a new rivalry emerges with a previous friend or neutral, and new rules of the road must be established. Under these circumstances, one state may unwittingly push another too far, because ambiguities as to national rights and obligations leave a wider range of issues on which each state may misjudge the other’s resolve. Norms of state behavior can come to be broadly understood and accepted by all states, even in multipolarity, just as basic norms of diplomatic conduct became generally accepted by the European powers during the eighteenth century. Nevertheless, a well-defined division of rights is generally more difficult when the number of states is large and relations among them are in flux, as is the case with multipolarity.

War is also more likely when states underestimate the relative power of an opposing coalition, either because they underestimate the number of states who will oppose them, or because they exaggerate the number of allies who will fight on their own side.¹² Such errors are more likely in a system of many states, since states then must accurately predict the behavior of many other states in order to calculate the balance of power between coalitions. Even assuming that a state knows who is going to fight with and against it, measuring the military strength of multistate coalitions is considerably more difficult than assessing the power of a single rival.

Miscalculation is less likely in a bipolar world. States are less likely to miscalculate others’ resolve, because the rules of the road with the main opponent become settled over time, leading both parties to recognize the limits beyond which they cannot push the other. States also cannot miscalculate the membership of the opposing coalition, since each side faces only one main enemy. Simplicity breeds certainty; certainty bolsters peace.

BALANCED VS. UNBALANCED MULTIPOLARITY

Unbalanced multipolar systems are especially war-prone for two reasons. The potential hegemons, which are the defining feature of this kind of system, have an appreciable power advantage over the other great powers, which means that they have good prospects of winning wars against their weaker rivals. One might think that a marked power asymmetry of this sort would decrease the prospects for war. After all, being so powerful should make the potential hegemon feel secure and thus should ameliorate the need to initiate a war to gain more power. Moreover, the lesser powers should recognize that the leading state is essentially a status quo power and relax. But even if they fail to recognize the dominant power’s benign intentions, the fact is that they do not have the military capability to challenge it. Therefore, according to this logic, the presence of a potential hegemon in a multipolar system should enhance the prospects for peace.

This is not what happens, however, when potential hegemons come on the scene. Their considerable military might notwithstanding, they are not likely to be satisfied with the balance of power. Instead they will aim to acquire more power and eventually gain regional hegemony, because hegemony is the ultimate form of security; there are no meaningful security threats to the dominant power in a unipolar system. Of course, not only do potential hegemons have a powerful incentive to rule their region, they also have the capability to push for supremacy, which means that they are a dangerous threat to peace.

Potential hegemons also invite war by increasing the level of fear among the great powers.¹³ Fear is endemic to states in the international system, and it drives them to compete for power so that they can increase their prospects for survival in a dangerous world. The emergence of a potential hegemon, however, makes the other great powers especially fearful, and they will search hard for ways to correct the imbalance of power and will be inclined to pursue riskier policies toward that end. The reason is simple: when one state is threatening to dominate the rest, the long-term value of remaining at peace declines and threatened states will be more willing to take chances to improve their security.

A potential hegemon does not have to do much to generate fear among the other states in the system. Its formidable capabilities alone are likely to scare neighboring great powers and push at least some of them to create a balancing coalition against their dangerous opponent. Because a state’s intentions are difficult to discern, and because they can change quickly, rival great powers will be inclined to assume the worst about the potential hegemon’s intentions, further reinforcing the threatened states’ incentive to contain it and maybe even weaken it if the opportunity presents itself.

The target of this containment strategy, however, is sure to view any balancing coalition forming against it as encirclement by its rivals. The potential hegemon would be correct to think this way, even though the lesser great powers’ purpose is essentially defensive in nature. Nevertheless, the leading state is likely to feel threatened and scared and consequently is likely to take steps to enhance its security, thereby making the neighboring great powers more scared, and forcing them to take additional steps to enhance their security, which then scares the potential hegemon even more, and so on. In short, potential hegemons generate spirals of fear that are hard to control. This problem is compounded by the fact that they possess considerable power and thus are likely to think they can solve their security problems by going to war.

Summary

Thus, bipolarity is the most stable of the different architectures, for four reasons. First, there are relatively fewer opportunities for conflict in bipolarity, and only one possible conflict dyad involving the great powers. When great powers do fight in bipolarity, they are likely to engage minor powers, not the rival great power. Second, power is more likely to be equally distributed among the great powers in bipolarity, an important structural source of stability. Furthermore, there is limited opportunity for the great powers to gang up against other states or take advantage of minor powers. Third, bipolarity discourages miscalculation and thus reduces the likelihood that the great powers will stumble into war. Fourth, although fear is constantly at play in world politics, bipolarity does not magnify those anxieties that haunt states.

Balanced multipolarity is more prone to war than is bipolarity, for three reasons. First, multipolarity presents considerably more opportunities for conflict, especially between the great powers themselves. Wars that simultaneously involve all the great powers, however, are unlikely. Second, power is likely to be distributed unevenly among the leading states, and those states with greater military capability will be prone to start wars, because they will think that they have the capability to win them. There will also be ample opportunity for great powers to gang up on third parties and to coerce or conquer minor powers. Third, miscalculation is likely to be a serious problem in balanced multipolarity, although high levels of fear among the great powers are unlikely, because there are no exceptional power gaps between the leading states in the system.

Unbalanced multipolarity is the most perilous distribution of power. Not only does it have all the problems of balanced multipolarity, it also suffers from the worst kind of inequality: the presence of a potential hegemon. That state both has significant capability to cause trouble and spawns high levels of fear among the great powers. Both of those developments increase the likelihood of war, which is likely to involve all the great powers in the system and be especially costly.

Now that the theory about the causes of war has been presented, let us switch gears and consider how well it explains events in Europe between 1792 and 1990.

GREAT-POWER WAR IN MODERN EUROPE, 1792–1990

To test offensive realism’s claims about how different distributions of power affect the likelihood of great-power war, it is necessary to identify the periods between 1792 and 1990 when Europe was either bipolar or multipolar, and when there was a potential hegemon in those multipolar systems. It is then necessary to identify the great-power wars for each of those periods.

System structure, we know, is a function of the number of great powers and how power is apportioned among them. The list of European great powers for the two centuries under discussion includes Austria, Great Britain, Germany, Italy, and Russia.¹⁴ Only Russia, which was known as the Soviet Union between 1917 and 1990, was a great power for the entire period. Austria, which became Austria-Hungary in 1867, was a great power from 1792 until its demise in 1918. Great Britain and Germany were great powers from 1792 until 1945, although Germany was actually Prussia before 1871. Italy is considered a great power from 1861 until its collapse in 1943.

What about Japan and the United States, which are not located in Europe, but were great powers for part of the relevant period? Japan, which was a great power from 1895 until 1945, is left out of the subsequent analysis because it was never a major player in European politics. Japan declared war against Germany at the start of World War I, but other than taking a few German possessions in Asia, it remained on the sidelines. Japan also sent troops into the Soviet Union during the last year of World War I, in conjunction with the United Kingdom, France, and the United States, who were trying to get the Soviet Union back into the war against Germany.¹⁵ Japan, however, was mainly concerned with acquiring territory in Russia’s Far East, not with events in Europe, about which it cared little. Regardless, the intervention was a failure.

The United States is a different matter. Although it is located in the Western Hemisphere, it committed military forces to fight in Europe during both world wars, and it has maintained a large military presence in the region since 1945. In those instances in which the United States accepted a continental commitment, it is considered a major actor in the European balance of power. But for reasons discussed in Chapter 7, America was never a potential hegemon in Europe; it acted instead as an offshore balancer. Much of the work on assessing the relative strength of the great powers during the years between 1792 and 1990, especially regarding the crucial question of whether there was a potential hegemon in Europe, was done in Chapter 8. The missing parts of the story are filled in below.

Based on the relevant distribution of power among the major states, European history from the outbreak of the French Revolutionary and Napoleonic Wars in 1792 until the end of the Cold War in 1990 can be roughly divided into seven periods:

1) Napoleonic era I, 1792–93 (1 year), balanced multipolarity;

2) Napoleonic era II, 1793–1815 (22 years), unbalanced multipolarity;

3) Nineteenth century, 1815–1902 (88 years), balanced multipolarity;

4) Kaiserreich era, 1903–18 (16 years), unbalanced multipolarity;

5) Interwar years, 1919–38 (20 years), balanced multipolarity;

6) Nazi era, 1939–45 (6 years), unbalanced multipolarity; and

7) Cold War, 1945–90 (46 years), bipolarity.

The list of wars for each of these seven periods is drawn from Jack Levy’s well-regarded database of great-power wars.¹⁶ However, one minor adjustment was made to that database: I treat the Russo-Polish War 1919–20) and the Russian Civil War (1918–21) as separate conflicts, whereas Levy treats them as part of the same war. Only wars that involved at least one European great power and were fought between European states are included in this analysis. Wars involving a European great power and a non-European state are excluded. Thus the War of 1812 between the United Kingdom and the United States, the Russo-Japanese War (1904–5), and the Soviet war in Afghanistan (1979–89) are omitted.¹⁷ Also excluded are European wars involving only minor powers. Finally, civil wars are not included in the analysis, unless there was substantial outside intervention by at least one European state, as there was in the Russian Civil War. The Spanish Civil War (1936–39) is omitted, although it is a close call.

Great-power wars are broken down into three categories. “Central wars” involve virtually all of the great powers in the system, and the combatants fight with tremendous intensity.¹⁸ “Great power vs. great power wars” involve either one-on-one or two-on-one fights. It should be noted that there is no difference between a central war and a great power vs. great power war in either a bipolar system or a multipolar system with three great powers. No such cases exist, however, in modern Eropean history. Finally, there are “great power vs. minor power wars.” During the 199-year period of European history under study, there were a total of 24 great-power wars, including 3 central wars, 6 great power vs. great power wars, and 15 great power vs. minor power wars.

The Napoleonic Era, 1792–1815

Europe was home to five great powers between 1792 and 1815: Austria, Britain/United Kingdom, France, Prussia, and Russia. Although France was clearly the most powerful state during this period, it was not a potential hegemon until the early fall of 1793, because it did not have the most formidable army in Europe before then.¹⁹ Remember that Austria and Prussia went to war against France in 1792 because it was militarily weak and therefore was considered vulnerable to invasion. France retained its exalted status as a potential hegemon until Napoleon was finally defeated in the spring of 1815. Thus, there was balanced multipolarity in Europe from 1792 until 1793, and unbalanced multipolarity from 1793 until 1815.

The period from 1792 to 1815 was dominated by the French Revolutionary and Napoleonic Wars. The first year of that conflict is categorized as a great power vs. great power war, because it involved only three great powers: Austria, France, and Prussia. Great Britain and Russia sat on the sidelines throughout 1792 and early 1793. The remaining twenty-two years of that conflict are categorized as a central war. France, which was attempting to become Europe’s hegemon, fought against Austria, Britain, Prussia, and Russia—although in different combinations at different times.

There were also three great power vs. minor power wars in the Napoleonic era. The Russo-Turkish War (1806–12) was basically an attempt by Russia to take Bessarabia, Moldavia, and Walachia away from Turkey, which was then called the Ottoman Empire. Russian victories in the last year of that war won Bessarabia, but not the other two regions. The Russo-Swedish War (1808–9) was caused by French and Russian unhappiness over Sweden’s alliance with the United Kingdom. Russia and Denmark went to war against Sweden and were victorious. Sweden had to surrender Finland and the Åland Islands to Russia. The Neapolitan War (1815) was fought between Austria and Naples. In the wake of Napoleon’s departure from Italy, Austria was determined to reassert its preeminence in the region, while the Neapolitan forces were bent on pushing Austria out of Italy. Austria won the conflict.

The Nineteenth Century, 1815–1902

Six great powers populated the European system for this eighty-eight-year period between the final defeat of Napoleonic France and the rise of Wilhelmine Germany. Austria/Austria-Hungary, the United Kingdom, France, Prussia/Germany, and Russia were great powers for the entire period. Italy joined the club in 1861. There was no potential hegemon in Europe between 1815 and 1902. The United Kingdom was clearly the wealthiest state in Europe during that period (see Table 3.3), but it never translated its abundant wealth into military might. In fact, the United Kingdom maintained a small and weak army for most of the period in question. The largest armies in Europe between 1815 and 1860 belonged to Austria, France, and Russia, but none of them possessed an army that was powerful enough to overrun Europe (see Tables 9.1 and 9.2).²⁰ Nor did any of them come close to having enough latent power to qualify as a potential hegemon.

The Prussian army became a formidable fighting force in the 1860s, vying with the Austrian and French armies for the number one ranking in Europe.²¹ France occupied that position for the first half of the decade; Prussia held it for the second half. There is little doubt that Germany had the strongest army in Europe between 1870 and 1902, but it was not yet so powerful that it was a threat to the entire continent. Furthermore, Germany did not yet have sufficient wealth to qualify as a potential hegemon. Thus, it seems fair to say that there was balanced multipolarity in Europe during the nineteenth century.

There were four great power vs. great power wars between 1815 and 1902. The Crimean War (1853–56) was initially a war between Russia and the Ottoman Empire, with the former trying to make territorial gains at the expense of the latter. But the United Kingdom and France entered the war on the Ottoman Empire’s side. Russia was defeated and was forced to make minor territorial concessions. In the War of Italian Unification (1859), France joined forces with Piedmont to drive Austria out of Italy and create a unified Italian state. Austria lost the war and Italy came into being shortly thereafter. In the Austro-Prussian War (1866), Prussia and Italy were arrayed against Austria. Prussia and Austria were essentially fighting to determine which one of them would dominate a unified Germany, while Italy was bent on taking territory from Austria. Austria lost and Prussia made substantial territorial gains at Austria’s expense. But German unification was still not completed. The Franco-Prussian War (1870–71) was ostensibly fought over Prussian interference in Spain’s politics. In fact, Bismarck wanted the war so he could complete German unification, while France wanted territorial compensation to offset Prussia’s gains in 1866. The Prussian army won a decisive victory.

There were also eight great power vs. minor power wars during the nineteenth century. The Franco-Spanish War (1823) stemmed from a revolt in Spain that removed the reigning king from his throne. France intervened to restore peace and the monarchy. Navarino Bay (1827) was a brief naval engagement with the United Kingdom, France, and Russia on one side and the Ottoman Empire and Egypt on the other. The great powers were helping the Greeks gain their independence from the Ottoman Empire. In the Russo-Turkish War (1828–29), the Russians went to war against the Ottoman Empire to support Greek independence and to make territorial gains in the Caucasus and other places at the Ottoman Empire’s expense. The First Schleswig-Holstein War (1848–49) was an unsuccessful effort by Prussia to take the duchies of Schleswig and Holstein away from Denmark and make them a German state.

In the Austro-Sardinian War (1848), the kingdom of Piedmont-Sardinia sought to drive Austria out of Italy and create a unified Italy under its own auspices. This attempt at liberation failed. The Roman Republic War (1849) broke out when France sent an army to Rome to restore the pope to power and crush the fledgling republic established there by Giuseppe Mazzini. In the Second Schleswig-Holstein War (1864), Austria and Prussia ganged up to finally take those disputed duchies away from Denmark. Finally, in the Russo-Turkish War (1877–78), Russia and Serbia sided with Bosnia-Herzegovina and Bulgaria in their effort to gain independence from the Ottoman Empire.

The Kaiserreich Era, 1903–18

There was no change in the lineup of great powers after 1903. The same six great powers remained at the center of European politics, save for the fact that the United States became a major player in 1918, when American troops began arriving on the continent in large numbers. Wilhelmine Germany, as emphasized in Chapter 8, was a potential hegemon during this period; it controlled the mightiest army and the greatest amount of wealth in the region. Thus, there was unbalanced multipolarity in Europe from 1903 to 1918.

This period was dominated by World War I (1914–18), a central war involving all of the great powers and many of the minor powers in Europe. There was also one great power vs. great power war during this period. In the Russian Civil War (1918–21), the United Kingdom, France, Japan, and the United States sent troops into the Soviet Union in the midst of its civil war. They ended up fighting some brief but intense battles against the Bolsheviks, who nevertheless survived. Finally, there was one great power vs. minor power conflict during this period: the Italo-Turkish War (1911–12). Italy, which was bent on establishing an empire in the area around the Mediterranean Sea, invaded and conquered Tripolitania and Cyrenaica in North Africa, which were then provinces in the Ottoman Empire (both are part of Libya today).

The Interwar Years, 1919–38

There were five great powers in the European system between the two world wars. Austria-Hungary disappeared at the close of World War I, but the United Kingdom, France, Germany, Italy, and the Soviet Union remained intact. There was no potential hegemon in Europe during these two decades. The United Kingdom was the wealthiest state in Europe during the first few years after the war, but Germany regained the lead by the late 1920s (see Table 3.3). Neither the United Kingdom nor Germany, however, had the most powerful army in the region between 1919 and 1938.²² Indeed, both states possessed especially weak armies throughout the 1920s and early 1930s. The German army certainly grew more powerful during the late 1930s, but it did not become the strongest army in Europe until 1939. Although it might seem difficult to believe given France’s catastrophic defeat in 1940, France possessed the number one army in Europe during the interwar years. But France had nowhere near the wealth and population to be a potential hegemon. Thus, there was balanced multipolarity in Europe during this period.

There were no great power vs. great power wars between 1919 and 1938, but there was one war between a great power and a minor power. In the Russo-Polish War (1919–20), Poland invaded a badly weakened Soviet Union in the wake of World War I, hoping to detach Belorussia and Ukraine from the Soviet Union and make them part of a Polish-led federation. Although Poland failed to achieve that goal, it did acquire some territory in Belorussia and Ukraine.

The Nazi Era, 1939–45

This period began with the same five great powers that dominated the interwar years. But France was knocked out of the ranks of the great powers in the spring of 1940, and Italy went the same route in 1943. The United Kingdom, Germany, and the Soviet Union remained great powers until 1945. Also, the United States became deeply involved in European politics after it entered World War II in December 1941. As discussed in Chapter 8, Nazi Germany was a potential hegemon from 1939 until it collapsed in defeat in the spring of 1945. Thus, there was unbalanced multipolarity in Europe during this period.

World War II (1939–45), which was a central war, was obviously the dominating event in Europe during this period. There was also one great power vs. minor power war: the Russo-Finnish War (1939–40). In anticipation of a possible Nazi attack on the Soviet Union, Stalin had demanded territorial concessions from Finland in the fall of 1939. The Finns refused and the Red Army invaded Finland in late November 1939. Finland capitulated in March 1940 and the Soviet Union took the territory it wanted.

The Cold War, 1945–90

There was only one great power left in Europe after World War II: the Soviet Union.²³ The United States, however, was determined to prevent the Soviets from dominating the region, so they maintained a massive military presence in Europe throughout the Cold War. This was the first time in its history that the United States stationed large numbers of troops in Europe during peacetime. Europe was therefore bipolar from 1945 to 1990.

There was no war between the two great powers during this period, but there was one great power vs. minor power war. In the Russo- Hungarian War (1956), the Soviet Union successfully intervened to put down an anticommunist revolt in Hungary.

ANALYSIS

Let us now sort this information to see how much great-power war there was in Europe when it was characterized by bipolarity, by balanced multipolarity, and by unbalanced multipolarity. In particular, let us consider the number of wars, the frequency of war, and the deadliness of the wars in each of those kinds of systems. The number of great-power wars in each period is broken down according to the three types of war described earlier: central, great power vs. great power, and great power vs. minor power. Frequency is determined by adding up the years in each period in which a great-power war was being fought. War need only be fought in some part of a year for that year to be counted as a war year. For example, the Crimean War ran from October 1853 until February 1856, and thus 1853, 1854, 1855, and 1856 are counted as war years. Finally, deadliness is measured by counting the number of military deaths in each conflict; civilian deaths are omitted.

Bipolarity seems to be the most peaceful and least deadly kind of architecture (see Table 9.3). Between 1945 and 1990, which was the only period during which Europe was bipolar, there was no war between the great powers. There was, however, one great power vs. minor power war, which lasted less than a month. Thus war took place in Europe during only one of the 46 years in which it was bipolar. Regarding deadliness, there were 10,000 deaths in that conflict.

Unbalanced multipolarity is by far the most war-prone and deadly distribution of power. During the periods when there was a potential hegemon in a multipolar Europe—1793–1815, 1903–18, 1939–45—there were three central wars, one great power vs. great power war, and five great power vs. minor power wars. A war was being fought during 35 of the relevant 44 years, and in 11 of those years two wars were going on at the same time. Finally, there were roughly 27 million military deaths in those conflicts (and probably about as many civilian deaths when all the murder and mayhem in World War II is taken into account).

Balanced multipolarity falls somewhere in between the other two kinds of systems. Consider that there were no hegemonic wars, five great power vs. great power wars, and nine great power vs. minor power wars during the times when Europe was multipolar but without a potential hegemon—1792–93, 1815–1902, 1919–38. In terms of frequency, war took place somewhere in Europe during 20 of the relevant 109 years. Thus, war was going on 18.3 percent of the time in balanced multipolarity, compared with 2.2 percent in bipolarity and 79.5 percent in unbalanced multipolarity. Regarding deadliness, there were approximately 1.2 million military deaths in the various wars fought in balanced multipolarity, which is far less than the 27 million in unbalanced multipolarity, but substantially more than the 10,000 in bipolarity.

CONCLUSION

These results appear to offer strong confirmation of offensive realism. Nevertheless, an important caveat is in order. Nuclear weapons, which were first deployed in 1945, were present for the entire time that Europe was bipolar, but they were not present in any of the previous multipolar systems. This creates a problem for my argument, because nuclear weapons are a powerful force for peace, and they surely help account for the absence of great-power war in Europe between 1945 and 1990. It is impossible, however, to determine the relative influence of bipolarity and nuclear weapons in producing this long period of stability.

It would be helpful in dealing with this problem if we could turn to some empirical studies that provide reliable evidence on the effects of bipolarity and multipolarity on the likelihood of war in the absence of nuclear weapons. But there are none. From its beginning until 1945 the European state system was multipolar, leaving this history barren of comparisons that would reveal the differing effects of multipolarity and bipolarity. Earlier history does afford some apparent examples of bipolar systems, including some that were warlike—Athens and Sparta, Rome and Carthage—but this history is inconclusive because it is incomplete.

This problem does not arise, however, when comparing the two kinds of multipolarity, because there were no nuclear weapons before 1945. It is apparent from the analysis that whether a multipolar system contains a potential hegemon like Napoleonic France, Wilhelmine Germany, or Nazi Germany has a profound influence on the prospects for peace. Any time a multipolar system contains a power that has the strongest army as well as the greatest amount of wealth, deadly war among the great powers is more likely.

The next and final chapter will consider China’s rise to economic and political power and the likely consequences of this rise for international politics in the twenty-first century.