The countries that suffered the most after World War I were the Central powers, as they represented the losing side. The Austro-Hungarian empire collapsed into a number of independent states, with the former hub of the empire, Austria, becoming a single country rather than continuing as the center of a multicultural empire. But the country that suffered the most if we add together the economical, physical, and most importantly, emotional aspects of the defeat was Germany.
Germany lost a good deal of territory to Poland, which angered and demoralized many German citizens. It also had to cede territory to France, Czechoslovakia, Belgium, and Denmark. The Germans were forced as well to agree to pay huge reparation payments. This caused a great deal of economic suffering after the war in Germany, as the government began to print money that was not backed by gold, leading to massive hyperinflation. The reduction of the army to no more than 100,000 troops also had a negative impact on what had been a heavily militarized economy. Many young men from lower class homes lost what had been a respectable and accessible career path in the armed services when those jobs were cut off. These disaffected men sometimes joined the freikorps, or rightwing militias, from which the Nazi Party recruited.
Germany suffered emotionally more than any other nation. It was the rising European power, poised at the turn of the century to rival Great Britain. After the war, this proud nation was humiliated, not only by the defeat, which took many citizens by surprise, but by being forced to sign the Versailles treaty, in which Germany had to take full blame for the war. Many Germans resented this as unfair and resented Britain's strong arm treatment in threatening to blockade German ports and cut off food supplies until the treaty was signed.
Stung by economic problems, loss of territory, and having a humiliating defeat rubbed in their faces in the worst possible way, the Germans eventually embraced Hitler, who promised a return to greatness.