I wrote a year ago about deciphering the data from a Neolithic grave site in Poland. I thought it likely at the time that these were *Corded Ware people killed by Yamnaya, or even more likely from those under pressure from Yamnayan expansion. It would be early for them directly, but they could have created pressure and disruption beforehand. An arrowhead in the shoulder of one of the victims is clearly from a long-established culture of farmers, descended from those who entered Europe in that expansion 3000 years earlier. The Corded Ware people were herders, and though they had long been in the area, their ways were still more nomadic, and conflict over resources was ongoing. But this was not the newest invaders raiding the previous invaders, it was the long-settled fighting back or defending against the encroachment of one of the many bands who had invaded long before and still roamed the area.
The Corded Ware people were an earlier group of steppe Indo-Europeans, not likely drawn from the ruling elite. They therefore may have struck out on their own from the Pontic-Caspian Steppe because of defeat or poor prospects. The Yamnaya who later pushed them out seem to be drawn from the more powerful groups.
*Again my caution about named categories. They are useful for putting structure on discussions, but they obscure as much information as they reveal. The Corded Ware people were likely many small groups, leaving at somewhat different times and taking different routes. They did not use all land they came upon, kicking the current residents out, but sought good pasturage, leapfrogging over areas, some inhabited, some not. They might settle among established groups in places they weren't using. Or they might create pasture by sending young men on ahead to burn out forest to be occupied a few years later, with the fire chasing out the previous farmers and whatever hunter-gatherers there were. They adopted the technologies they encountered unevenly. Though they stayed in contact with each other, they fought with each other and became different. They married with, or captured brides from different tribes. The model to think of when encountering the word migration is to think of Europeans (and Africans, Asians) coming to the New World, not because it is typical, but because it is varied over a 500-year period. You can't sum up what happened in a sentence or a paragraph or just draw a single fat arrow on the map to illustrate it. So too with prehistoric migrations.