Jared Diamond's book, "Guns Germs and Steel" documents the history of this kind of dispacement of one culture by another via conquests and invasions. Jared pursued the question of why westerners have so much, while some native people had so little. He sought to explain inequality.
The main culprits were: Guns, Germs and Steel - memes, pathogens and more memes - or, in other words: symbiosis, symbiosis, symbiosis!
Jared Diamond's book is all about the importance of symbiosis in human evolution.
Indeed, the pathogens Diamond talks about were spread by hitchhiking on shipbuilding memes. So, if you look at the ultimate causes, Guns, Germs and Steel boils down to memes, memes and more memes.