When you think of war, you usually think of organized states, or at minimum peoples with moderately sophisticated modes of production, agriculturalists or pastoralists. But hunter-gatherers manage as well. Not just war, but decisive war, the kind that that obliterates the enemy and results in a major geographic expansion. Before the Eskimos, there was a different population living in arctic North America and Greenland, the Dorset culture. Over a fairly short period, between 1000 AD and 1500 AD, the Thule (ancestors of modern Inuit) moved east, replacing the Dorset. It looks as if the Thule didn’t mix much with the previous occupants either: we have an early Dorset genome that looks very Na-dene-like, while the Eskimos are not. The conflict was recent enough to leave legends among the Eskimo: they say the first inhabitants were giants, taller and stronger but easily scared off.
While we’re at it, the Na-dene managed to pushed down from western Canada and Alaska all the way into the Southwest, leaving the Navaho and Apache where they are today. Although the Navaho surely mixed with generic Amerinds, they look different, more Asian, so they likely still have a lot of their ancestry coming from the second, Na-dene migration into North America.
Neither of these stories sound very much like like Excoffier/Currat diffusion models.
This has me wondering how many waves of population replacement occurred before agriculture in Europe. We know that homo sap replaced the Neanderthals, but we sure don’t know that population replacement stopped there. There were certainly waves of immigration in the Neolithic – middle Eastern farmers and probably Indo-Europeans – but what about earlier?