Answer:
World War I and its aftermath laid the groundwork for World War II, primarily through the punitive measures and territorial adjustments dictated by the Treaty of Versailles. The treaty imposed heavy reparations and territorial losses on Germany, leading to a severe economic depression and engendering deep resentment among the German populace. The harsh conditions, including the "war guilt clause" which held Germany and its allies responsible for the war, created a sense of national humiliation. This atmosphere proved fertile for extremist political movements, notably the Nazi Party under Adolf Hitler, who promised to restore Germany's pride and status in the world.
As Hitler and the Nazis rose to power, they violated several provisions of the Treaty, such as reoccupying the Rhineland and pursuing rearmament, with minimal pushback from the international community. The appeasement policies of major European powers, notably Britain and France, emboldened Hitler further. The annexations of Austria and the Sudetenland, and later all of Czechoslovakia, under the guise of promoting German nationalism and correcting the "wrongs" of the Treaty of Versailles, went largely unopposed. These acts of aggression set the stage for the invasion of Poland in 1939, leading directly to the outbreak of World War II.