The “interwar years” refer to the pivotal 20 years that fell between the end of World War I and the beginning of World War II. The effects of World War I were profound for Europe. Ten million were killed, and twice that number wounded. To put this number in perspective, all the wars of the 100 years prior had only claimed a total of 4.5 million lives. What would come to be called the “first modern war,” had caused the destruction of an entire generation, leaving many survivors psychologically scarred, making it difficult to live normal lives.

In addition to the toll taken on European life, financial insecurity plagued all of Europe during the interwar period, with both the victorious Allies and the defeated Central Powers were saddled with enormous national debts. The very land of Europe was physically devastated, and the three great European empires—Germany, Austria-Hungary, and the Ottoman Empire—had been toppled and lay in ruins. Soldiers of both sides returned home to devastation and found only rampant unemployment and despair. In almost every nation, the response was internal political conflict and social instability.

The diplomatic results of World War I greatly influenced the nature of European affairs during the interwar years. The Paris Peace Conference drew the boundaries for new, independent states in Eastern Europe, but, in many cases, these new states were not economically viable, due to both the destruction of the war and past reliance on the economies of their former empires. Already unused to democracy and independence, these countries were also divided internally into factions and ethnic group ready to be radicalized politically. As a result, the ideologies of both fascism and communism attracted more followers during the interwar years than ever before. All of this made the task of good government difficult, if not impossible, throughout Eastern Europe. Instability and poorly operating, often-dictatorial governments were typical of these states, making them easy targets for a rearmed Germany during the late 1930s.

Germany, for its part, was incapacitated by both the war and its settlement, in which it was scapegoated as the conflict's aggressor. The Treaty of Versailles ordered the military and economic dismemberment of the German states along with impossible reparations payments to Britain, France, and the other allied nations. France, having suffered the greatest destruction at the hands of the Germans, was adamant about keeping Germany both weak and accountable through reparations. As a result, Germany suffered starvation, mass unemployment, and rampant inflation, all made even more unbearable by the Great Depression. 

Naturally, Germans reacted bitterly toward their foreign oppressors and dreamed of a return to the glory of the German Empire. It was this dream which permitted the ascension of Adolf Hitler and the Nazi Party to power in Germany, who promised all that and more. Under the Nazis, Germany rearmed and began a program of European conquest. At first, the former Allies were hesitant to intervene, hoping to avoid a second war, but it soon became clear that appeasement could not last. Just 20 years after the “War to End all Wars,” Europe fell again into devastating conflict.