I have recently mentioned the effects of disease on history, most notably the Justinian Plague in the 6th C and the Great Plague in the 14th C. Plus, I am also always mentioning the Yamnaya, the Indo-Europeans coming in from the Eurasian Steppe and overwhelming Europe. I can't find that I have put them together. They should be put together. The Yamnaya asserted such dominance over time that two-thirds of European males have one of their their y-haplogroups, R1a or R1b. There is debate over how much of this is battle and raiding and how much outcompeting in more long-term ways like better food acquisition. If you like this in the form of a science-story about raiding males and canny females, here is one.
To this mix disease should be added, specifically plague. The Stone Age cultures in Europe may have been decimated by disease before the raiders arrived, which makes and conquering considerably easier. That version of the plague may have originally come from Central Asia, and the Yamnaya may have had some resistance to it. Disease often spreads ahead of a slowly-migrating people, as in the European arrival in the New World. Some version of the plague is known to have arrived before them, in Sweden.
This was a less deadly plague than what we are used to thinking about, because it could not be spread by fleas. That adaptation of the plague that killed us better did not occur until about 1000 BC. However, it could still be spread by coughing and kill you very badly. I wrote recently about the first farmers coming in, only partly competing with the hunter-gatherers, partly occupying different niches and living alongside each other for centuries, and something similar seems to have happened to them when the Indo Europeans came in. The new arrivals did become dominant. We have considerable evidence that they were a violent, raiding culture who used the horse and the axled wheel to exploit regions efficiently. Yet the previous inhabitants also persisted, some up in the mountains, others along the shore exploiting marine resources, others still growing grains.