While King William was sure that Gravelotte-St-Privat and the isolation of the Army of the Rhine marked the decisive point of the campaign, Moltke was not so sure. On the morning of 19 August he turned his mind westward to MacMahon at Châlons.
Having rested his men on the 19th and 20th, Moltke removed the Guard, IV and XII Corps from the Second Army of the Meuse and left its remaining four corps together with those of First Army under Frederick Charles to invest Metz. Third Army and the new Army of the Meuse under the Crown Prince of Saxony headed west on the 21st to close the campaign. Meanwhile Steinmetz was finally removed from doing any further mischief by being ‘promoted’ to Governor of Posen.
Meanwhile, on the French side Napoleon had been with MacMahon at Châlons since the 16th where a new army was being formed around the nucleus of I, V and VII Corps. With the new XII Corps of regulars under General Trochu, plus newly joined recruits and depot battalions to fill the gaps left by the frontier battles, and even eighteen battalions of the Guard Mobile of the Seine, an army of 130,000 men and 423 guns had been created by 21 August. In Paris, news of the early defeats and Bazaine’s entrapment at Metz lead first to public gloom and then to fury. Repulican riots began and confidence in the Imperial regime plummeted. Consequently the Empress and Palikao bombarded the Emperor with messages insisting that he could not lead the Army of Châlons back to Paris as a defeated Emperor — the regime would collapse. With the public demanding that Bazaine be relieved, added to the need for ‘victory’, the subsequent course of events was dictated to MacMahon and Napoleon.
Accompanied by Napoleon, MacMahon’s Army set out for Rheims and then Montmedy in an attempt to swing around Moltke’s northern flank and relieve Metz. If such a move could have been successful, it would have also placed the French across the German lines of communication, with a heavily fortified Paris to the west. Yet by the 24th Moltke was fully aware of MacMahon’s movements and he quickly seized the opportunity to encircle and destroy him.
The numerically and morally superior German forces swung north-west and on the 30th the cavalry patrols of Third Army found MacMahon fifteen miles south-east of Sedan at Beaumont-sur-Meuse where a small action ensued. With part of his army beaten at Beaumont on the 30th, MacMahon fell back to Sedan to regroup, not realizing that he was falling into a trap. On 1 September, with some 100,000 demoralized men and supplies for only a few days, MacMahon found himself encircled on 1 September by some 200,000 men. The Battle of Sedan was a foregone conclusion, desperation and honour being the motivating factor on the French side.
As MacMahon and the Emperor surrendered with the last army of the Second Empire, the campaign begun only four weeks earlier ended. The Empire itself collapsed on 4 September and the newly proclaimed Republic then endured the Siege of Paris and the desperate campaigns of the autumn and winter. On 28 October Bazaine had finally surrendered the entire Army of the Rhine at Metz, the last outpost of the Empire.
While France underwent political revolution and military defeat, Germany became an Empire on 18 January 1871 in the reflected glory of victory. The war itself ended on 23 January as France accepted defeat and humiliation.