Western science continued to advance in the twentieth century. New scientific theories such as Einstein’s Special and General Theories of Relativity, Planck’s Quantum Theory, Von Neumann’s Game Theory, Shannon’s Information Theory, and Wilson’s Plate Tectonic Theory led to significant advances in physics and astrophysics, economics, telecommunications and computing, and earth science. Development also continued from earlier theoretical breakthroughs in subjects like genetics, evolution, probability, logic, chemistry, and statistics. This kind of work supported a vast number of more specific discoveries, many of which stemmed from a desire for knowledge but resulted in practical technological designs and production. Pure science, in conjunction with more results-oriented research and development, thus became an industry in its own right; governments, corporations, and universities supported sciences in the hope of producing another breakthrough invention or method. The Nobel Prizes, first awarded in 1901, have become a coveted worldwide marker of national and institutional prestige in the sciences.
During the early twentieth century, technological inventions stemmed from the nineteenth century’s drive to improve devices that ease or replace human labor. Electric motors and internal combustion engines were more practical and portable than steam engines. Automobiles and airplanes supplemented the railroad as transportation. Radio and television continued what the telephone and telegraph had started in communications. Electric appliances in general began to replace servants in households and the workplace. Huge infrastructure investments, like power grids, highways, and communication networks, spread from wealthier areas to further parts of the world.
The second half of the century saw radical breakthroughs; the new field of Information Technology allowed exponential increases in productivity by having machines control other machines. Analog devices like mechanical computers and automated switchboards in the early decades were revolutionized by electronic circuitry developed during World War II. Digital computers and similar equipment exploded onto the technological landscape in the 1960s; these were increasingly miniaturized, and then applied to every form of mechanical device for governments, businesses, and consumers. The internet, connecting the world’s computer systems and users into a single general information-sharing entity, began the next wave of transformation of society in the 1990s.
Cheap and easily adapted technology compressed the amount of time and money it took to modernize an undeveloped region. Accordingly, the industrial revolutions of the later twentieth century in Asia, Africa, and Latin America were faster and more extensive than Europe’s and North America’s revolutions had been a century earlier. The general trend of automated control of mechanized production led to huge shifts in the employment of the working classes in developed countries. Factory work and resource extraction, as well as farm work, now used far fewer workers, while lightweight semi-skilled and service industries expanded to provide more consumer services. Rapid transport and communication, as well as liberalized trade conditions, also allowed these industries to be located in lower-wage world regions, further stressing the prospects of the lowest classes in higher-wage nations. Mass production of goods and energy around the world, however, led to large-scale environmental issues of ecological pollution, public health, and toxic disposal. The production of the world’s power supply almost entirely from carbon combustion (the burning of oil and coal) began to change the global climate itself.
The human population of the world has grown tremendously in the past century, from approximately 1.6 billion to 6.1 billion people. Improved public health was facilitated by the use of sewage systems, and new medicines, including vaccines; similarly, education increased the life expectancy of families. Technological advances in agriculture, known as the Green Revolution, introduced chemical fertilizers and high-producing seeds to the developing world. This postwar phenomenon fed the growing world population and prevented the famines that have cut short earlier eras of peace and prosperity.
Despite increased life expectancy, birth rates actually went down in developed societies as families invested more resources in raising fewer children. Thus, the population growth in the industrialized West and Japan stabilized by the end of the century, while the increase was more dramatic in the poorer regions in Asia and to the South. China and India currently have populations over a billion, despite strict family planning policies in China and birth control programs in India.
While traditional killer diseases such as malaria, cholera, smallpox and tuberculosis have come under control due to international public health efforts, population growth in some areas has been affected by new epidemic diseases that have spread more easily in the increasingly interconnected twentieth-century world. The influenza pandemic of 1918 killed 75 million people, and since the 1970s, HIV/AIDS has killed over 30 million people. In addition, in the wealthier parts of the world, longer lives, changing diets, and toxic environments have led to increases in other types of diseases such as diabetes, heart disease, and certain kinds of cancer.
Though migration has been a theme throughout world history, it has increased across the past century. This includes internal migration (such people moving from rural to urban areas, or fleeing urban areas due to civil strife) and external migration (such as people migrating long distances and across borders, or in search of better economic conditions). The biggest factors have been imperialism, industrialization, and war.
| Cause | Effect |
| Imperialism | In the early twentieth century, colonial empires expanded plantation crops for a growing world market; with slavery no longer an acceptable system, contract labor was imported to work the fields. For instance, British developments in the Caribbean and Indian Ocean basins attracted millions of Chinese and Indian workers. |
| Industrialization |
From its inception, industrialization has depended on a working class drawn from rural area. The pattern seen in nineteenth-century Europe and America has been repeated across the southern tier (Latin America, Africa, southern Asia) as well as in Soviet Russia and modern China; hundreds of millions have moved to urban areas for work. The resulting explosion of urban areas, including industrial slums and social unrest, parallels earlier history in the West. |
| War |
The extensive wars of the twentieth century’s global conflicts have produced millions of refugees and displaced persons as borders changed, populations were expelled, workers were summoned to relocated war industries, and people evacuated devastated cities. Similar movements took place in the post-colonial adjustments and wars of liberation that characterized the Cold War era. |
| Post-Imperialism |
Some external migrations have followed from past imperialism. Communities of Algerians and Vietnamese, for example, have settled in Paris; Pakistanis and Jamaicans have settled in London; Filipinos, Cubans, and Iranians have found havens in U.S. cities. This unexpected consequence of imperialism has resulted in new cultural identities for the host nations, as well as exclusionary reactions like anti-immigration movements. |
The globe’s huge population growth, combined with continuing industrialization, has contributed to significant environmental problems in this century that include the overuse of natural resources, contamination by pollution, and losses of plant and animal species. Many oceanic fish species are significantly depleted to the point where governments have had to prohibit commercial fishing. Unique flora and fauna species have disappeared with the destruction of tropical forests for slash-and-burn agriculture and timber operations. Smog has polluted many city areas, which has increased lung diseases, which can kill vulnerable populations. Water pollution has restricted fresh water access for many, particularly in developing nations. The damming of rivers for power, flood control, or irrigation has also interrupted aquatic species’ life cycles; in some cases, so much water is drained off for irrigation projects that the watercourse fails to reach the sea. The increased use of petroleum and heavy metals like mercury in industrial production has also contributed to the pollution of entire ecosystems. Human population growth and prosperity has led to dramatic increases in the amount of trash produced by industrialized societies. Non-degradable and often toxic, this waste ends up in landfills or is transported to less developed countries to be salvaged.
Scientists have established that the industrialized world’s massive increase in carbon-based fuels and other greenhouse gases has begun a gradual rise in overall global temperatures. This climate change is projected to have worldwide effects on the ecologies and food supplies of all human habitats, from droughts in some areas to increased precipitation in others. A broadly threatening aspect is rising ocean levels from melting ice caps, which will threaten the viability of most cities that are located on seacoasts.
In reaction to these threats, environmentalism has grown in visibility and political power; this movement to protect and wisely use our natural resources first appeared in the late 19th century. Since the 1970s, when postwar development led to visible environmental degradation, most national governments in the West have set up agencies to monitor industrial use of resources and to regulate waste products. The post-Communist states and developing nations have been slower to follow, for fear that excessive regulation will slow national growth. Countries with large natural territories have created regional and national parks and wildlife refuges in order to keep such areas intact for future generations of wildlife and people. International organizations, such as Greenpeace, the Sierra Club, and the World Wildlife Fund, work to protect the environment both through direct action and by lobbying governments for legal action.