It is not at all true that other places outside of Europe were “calmer”, if by calm you mean peaceful.

Asia: I’m sure you have heard of the original empires of Mesopotamia, like Sumer, Akkad, Assyria, Babylon, Persia, and others. They were absolutely brutal, had some of the first standing armies, and practically invented genocide on a mass scale. Then there is the Mongolian Empire and other steppe empires like the Golden Horde, all of them famous for industrial-scale mass slaughter. And, of course, there is the ethnic cleansing of most of present-day China by the Han people. In Japan, early mainland immigrants wiped out the Ainu. In India, you have the invasion by northern Aryan tribes who slaughtered and dominated the Dravidian people, the remnant of which are still in southern India and Sri Lanka. Those are just a few of the better known ones.

Africa: There was all-conquering Egypt, of course, and many others south of the Sahara I’m sure, though they are less well-documented for obvious reasons.

Americas: The Inca and the Aztec were significant conquering empires. We are limited by a lack of written language in most of the Americas, but it is well-documented both orally and archaeologically that North American tribes displaced one another with regularity.

In terms of slavery…nearly every civilization prior to the industrial revolution used slave labour extensively, because that was the way to get work done before the advent of machines. The institution of slavery varied significantly across time and place, from the death sentence of working to death in Roman salt mines to well-educated slaves who were clerks and teachers. Slavery was a major Roman institution, but it was (and still is) rampant across Asia and Africa. The Americas also had slavery.