Answer:
1. Treaty of Versailles - The Treaty of Versailles, which ended World War I, was considered by many Germans to be a humiliating treaty that unfairly punished Germany by making the country responsible for causing the war and imposing severe financial reparations. This treatment of Germany, coupled with the economic depression of the 1930s, created a fertile environment for the rise of nationalism and fascist ideologies.
2. Appeasement policy - The policy of appeasement, pursued by the Western powers in Europe, is often cited as a major cause of the Second World War. This policy involved making concessions to aggressive, expansionist governments in order to avoid conflict. The Western powers allowed Germany to annex Austria and then the Sudetenland (part of Czechoslovakia) without resistance. This emboldened the German leader, Adolf Hitler, and eventually led to the invasion of Poland in 1939.
3. Rise of fascism - The rise of fascist regimes in Europe during the 1930s was a major factor in the outbreak of World War II. In Germany, Italy and Japan, strong, nationalist leaders and political parties came to power that aimed to reassert their country's power and prestige through military action, imperialism and territorial expansion. The belief in extreme nationalism, militarism, and the supremacy of their nations led to aggression against other countries and ultimately, war.