The Hohenzollern dynasty collapsed because Germany was suffering an economic collapse during the war. The allies had blockaded German ports, so no foodstuffs could enter the country.Germany gained a brief respite after the surrender of Russia at Brest-Litovsk. Shortly thereafter, the Germans launched a major offensive against French lines, but the offensive was turned back within 35 miles of Paris at the Second Battle of the Marne. Allied success was largely the result of the infusion of fresh American troops who did not suffer from the war weariness that plagued the other forces. Both sides were weary of the war, but it was the Germans who cracked first.
The German people were forced to eat turnips; which had previously been grown only to feed to livestock. Wilhelm II contacted President Woodrow Wilson and asked for terms of peace; but Wilson replied that he would only negotiate peace with the democratically elected government of the German people. Revolution broke out in Germany after the surrender of Austria-Hungary, Wilhelm abdicated and a Social Democratic majority government was elected.The German Social Democrats accepted defeat and ended the war as soon as they took power. This ended the loss of morale among the troops and prevented the regular army from disintegrating.