Mankind is violent.
I've recently read a book called Guns, Germs and Steel. It's highly enlightening. Man is more violent than most of us want to admit. Our history and our pre-history is one long tale of murder. Forget recent history ... even back two hundred years. Heck ... two thousand. Throughout the dim past, the archeologists are now proving, the agriculturists wiped evey hectare they trod upon of the indiginous hunter gatherers.
In New Guinea, to this day , if two men meet in the forest and they can not establish that they know someone in common, a distant cousin usually, they will more than likely fight to the death.
When the ancestors of the Polynesians had a war it was often to the death of every man of the oposing army. Often the women and children as well.
The Norse terrorized all of coastal Europe for a thousand years.
We all know about Gengis Kahn.
Actually the West is less violent than any culture the world has ever known ... but this anomaly is passing. It doesn't work. Sensible people sooner or later are forced to admit ..... when your neighbor vows to kill you the smartest thing to do is kill him first.
But some groups, cultures, and religions are more violent than others. Some are very peaceful. The Islamists are violent. It's part of their culture.