What event over any period of time has killed more people?

You could say WWII which killed 65 million during the war and include the ten million Germans killed after the war too. During the war 20 million Germans were killed and ten million Germans killed after the war. This would be the greatest amount of suffering by anyone. What caused this? You would have to say Communism which after taking control of Russia they took Poland and Poland was right next door to Germany. So could we assume the Commies were filtering into Germany to take that country too? If that's the case what would have happened to Germany had they not armed themselves to fight the Communists? It's safe to assume Communism caused WWII and not Hitler.