This is a fascinating topic ! From a cultural perspective, it ties in with a personal theory I've got....

For at least the last 40,000 years, people have generally moved into Europe from east to west. It's a 40,000 year history of waves of migration and invasion, most of it not very peaceful. Each wave has had to learn how to overcome the settled remains of all the waves that went before it (some integrated, some just a veneer of ruling class over what was already there). So it's very much a Darwinian process.

By around 1500AD, the blended population of Europe had developed the most efficient martial culture on earth, and one that was ruthless in adapting technology to war. A good example is gunpowder - invented by China and used to make primitive rockets and pretty fireworks, turned into cannons and muskets by Europeans.

Europeans got so good at fending off invaders that they started winning, started pushing back, and built themselves colonial empires. I'm not saying that's a good or bad thing, it just is. They were just simply better at killing people, and more resistant to diseases bought by invaders (just ask the poor Incas...).