What were the three main causes of world war 2?

1. Treaty of Versailles which  forced Germany into accepting full blame for WWI. 
2. The Rise of Hitler to power 
3. The Annexation of Austria--- The allies allowed Germany to annex Austria-1938-(which was forbidden by the Treaty of Versailles) followed by the allies allowing Germany to take the Sudetenland lands (Czechoslovakia ) without permission of the Czechs -- which was done to appease Hitler.