There are many causes for WW2. First the treaty of Versailles was way to harsh. Italy felt like they where cheated out and they deserved more after WW1. Poland was splitting germany in 2 from mainland and east prussia which made germany want to invade poland to connect the 2 land masses. Some key events in WW2 would be operation Barbarossa, bombing of pearl harbor and D-day. Those 3 events lead to Germany's downfall.