What are three of the most significant casues of World War 2?

The 3 key causes of WW2 can be debatable but most would say

1. Treaty of Versailles forced Germany into accepting full blame for WWI. This caused Germany to loose some of its lands, and forced them to pay for war damages to countries like France and Britain etc. In order to pay, Germany printed more money, which led to hyper inflation rates in Germany which lead to the great depression.
2. Rise of Hitler to power. by seeking flaws to exploit within the Wiemar Republic. Elected Chancellor 1933 and becomes President after death of Hindenburg 1934.
3. The allies allowed Germany to annex Austria-1938. (forbidden by the Treaty of Versailles) followed by the allies allowing Germany to take the Sudetenland lands (Czech) without permission of the Czechs, which was done in hopes of appeasing Hitler.