Question

What were some of the causes for WWII?

Answer 1

There's quite a few, but nationalism would be a big one as it eventually led to the practice of fascism in countries like Italy, Germany, and led the military to run things over in Japan in order to secure by aggression what resources they needed.

The Treaty of Versailles is another since the long term effects of its punitive measures against Germany embittered an entire generation, eventually opening the door to demagogues like Hitler to take advantage by promising to restore the nation to a position of prestige instead of humiliation.

Appeasement is another since it only served to feed Hitler's perception that the West was weak and he was free to take what he wanted when they kept bowing to his demands.

Ultimately, the trigger that started WW2 (in Europe) was Hitler's invasion of Poland. Both France and England declared war on Germany after that, and the rest, as they say, is history.