There are lot of discussions regarding the way Proto Indo Europeans spread from their homeland in pontic-caspian steppes. Or, more accurately - a lot of discussions regarding the nature of this expansion - if it was peaceful or violent. It seems that more and more evidence is emerging (like link supporting M.Gimbatus ideas of violent and intentional conquest of early european farmers by scary cruel to be indo europeans. The picture seems to fit well in the usual perception of gentle and nice farmers - mostly because they’re settled and associate with modern us and evil pastoralist associated with some kind of brutal nomadic savages. The situation when settled people are rampaged by nomads is actually will repeat periodically with last case being Mongol invasion. So why does it happen? The settled people should have better technologies, better social organization, better knowledge of the landscape to the least, and yet each time they fall to the invaders. Why? because until the very recent times andantage in technologies was never a decisive factor, you had to be able to show no mercy and kill them all, that's it