what are the key events during the civil war
that many people had got killed and also people had to get separated
one of them is the sinking of the Luisitania
the nuking of japan
world war 2 :P
World War 1 World War 2.
World War I and the Great Depression
World War 1 for example.
the assasination of Arch Duke Ferdinant.
Thats quite a big question considering you haven't mentioned which war. I assume World War 2?
Historically the biggest events could be considered to be World War I and World War II. There are many other major events that have happened in Europe going back over centuries.