Tons of Africans in Africa live peacefully, without short tempers or violence. Sure, some warlords reign terror on everyone else there, but the same happens in every 3rd world country. Look at South America. And some random acts of violence occur, but look at the Native Americans when the Euros came. The natives would lead random war parties against themselves and against the Euros. The Euros thought they were barbarian, vicious b*stards, but they just didn't understand why those things happened.
In actuality, Native Americans were quite peaceful before the Euros came along. Same could be said for Africans in Africa.
You should read "Ishmael" by Daniel Quinn. He explains very well why tribal violence occurs. We're no different than any other animal in the animal kingdom. When we lived in tribes, we had to compete for resources. If there were too many people, people would go hungry and die. Intermittent violence between tribes was to maintain population control.