Many factors lead to World War II, and many of them were either directly or indirectly linked to World War I, including dissatisfaction over the Treaty of Versailles, the rise of Fascism and Hitler's rise to power and his eventual aggression, using his Nazi party to fulfill a mission to unite all German-speaking people.
The Treaty of Versailles, which effectively ended World War I, perpetuated dissatisfaction throughout Germany and Austria by placing the responsibility of World War I almost entirely on them. As a result, the Germans were harshly penalized through the treaty. They were ordered to pay fines for the war as well as to disband their military. The new government was unable to stabilize the economy and it collapsed. Fascism had been rising in popularity in southern Europe since shortly after World War I ended, and Hitler was inspired to adopt many fascist policies for his Nazi party. The Nazi party promised the repressed Germans the hope of finally being able to rebuild successfully. Once the Nazis took control of the German government in 1933, Hitler called for the remilitarization of Germany, which was a direct violation of the Treaty of Versailles. Hitler was able to move forward with his plans to build one great Germany with little intervention from other European nations. Without steps taken to effectively stop him, Hitler began invading other countries and taking over territory. The growing land disputes between Hitler and other European nations effectively led to the beginning of World War II.