Peace and an end to the war did not come easily. Victory over revolutionary Russia had temporarily boosted sagging German morale, and in spring 1918 the German army attacked France once more. The German offensive was turned back in July at the Second Battle of the Marne, where 140,000 fresh American soldiers saw action. Adding 2 million men in arms to the war effort by August, the late but massive American intervention decisively tipped the scales in favor of Allied victory.

By September British, French, and American armies were advancing steadily on all fronts. On October 4 the German emperor formed a new, more liberal German government to sue for peace. As negotiations over an armistice dragged on, the frustrated German people rose up. On November 3 sailors in Kiel (keel) mutinied, and throughout northern Germany soldiers and workers established revolutionary councils on the Russian soviet model. Austria-Hungary surrendered to the Allies the same day. With army discipline collapsing, Kaiser William abdicated and fled to Holland. Socialist leaders in Berlin proclaimed a German republic on November 9 and agreed to tough Allied terms of surrender. The armistice went into effect on November 11, 1918.