What cause the holocost

For starters, it is Holocaust.

The Holocaust (Better known as World War 2) was caused by Adolf Hitler, and his mission to eliminate anyone who was not Aryan race. (Aryan is a word the Nazis made up, which has the common misconception of blonde hair and blue eyes)

This was mainly a slaughter of Jewish people, but also slaughtered many others.

The meaning of the word holocaust is actually "Destruction or slaughter on a mass scale, usually by fire or nuclear war"