I don't want to give you an essay but I can give you some main ideas that you can turn into an essay.
First, WWII initially started by the Nazi's invasion of Poland on September 1, 1939. Hitler essentially just wanted complete dominance over Europe, so this is what led the Nazis to continue their invasions into other countries.
Many people were captured and put into POW or concentration camps, where some managed to escape or some just remained there until the duration of the war. The most comment method of escaping a POW camp was tunneling out.
Effects of WWII could be the historical even of the Holocaust, where an estimated 10 - 17 million people were murdered by the Nazis. This had a very negative impact on the world. You can obviously do more research on that as well.
I hope this got you off to a good start.
