Question

What happened in WWII

Answer 1

One is it lead to the program of exploring outer space. The U.S and the Soviet Union was going against each other. The development of the nuclear bomb and the war against Japan. Hitler dictating over Germany and had all the
Jewish's being imprisoned in camps. The woman's movement rights also happen.
There's more but you need to be more specific with your question. 

Answer 2

Ah yes, the second world war. It lasted from 1939-1945.
so a scattered overview would be that
- we (US) got involved in 1941 because of the pearl harbor bombing where japan attacked us forces.
- Hitler hates the Treaty of Versailles (made previously in WW1 placing full blame on Germany) so he rebuilds the military, and starts to invade places such as Poland to expand (thus violating the treaty)
-The whole anti-semetism sparked, anyone opposing the Nazis would be punished...blah, blah.
- Britain and France declared war on Germany
(Hitler failed in his attempt to take over Russia (literally same thing that happened to Napoleon))
- Many other invasions (Italy, Poland  etc)
- D- day (the day the allied forces would attack German forces)
Oh, I almost forgot to mention the involvement of japan. 

This is much more of a broader subject. I can go right into the holocaust, and then the events after leading to the cold war and arms race. 

Let me know if you need more info, or more details.