No event more precisely marks the transition from the nineteenth to the twentieth century than the First World War. Its length, cost, and impact anticipated by practically no one, this conflict, soon to be referred to as the “Great War,” saw the Germans checked in the West in their rush to victory in 1914. Something of a stalemate developed there in the following years while Germany and its allies defeated in turn their enemies in the Southeast, South, and East. The Romanov dynasty in Russia, which had held onto the unoccupied parts of that country a century earlier when the forces of Napoleon had taken Moscow, lost its grip on the country in February 1917; the succeeding Provisional Government was unable to consolidate its rule and was overthrown by the Bolsheviks in October of the same year.

One reason that the Germans had assisted the Bolsheviks was the hope that they might take Russia out of the war, and this hope was realized as fighting stopped on the eastern front. The Germans could now resume major offensive operations in the West, but they were unable to inflict a decisive defeat on the Allies. Two factors were primarily responsible for this failure: the prior exertions of the war had weakened Germany considerably, and she had deliberately drawn the United States into the war against herself by an unrestricted submarine campaign which was supposed to knock out Great Britain but failed to do so.

Under these circumstances, as the Western Allies turned to a series of counteroffensives, the Germans were forced to fall back.