Kurgan hypothesis
According to Gimbutas' version of the Kurgan hypothesis, Old Europe was invaded and destroyed by horse-riding pastoral nomads from the Pontic-Caspian steppe (the "Kurgan culture") who brought with them violence, patriarchy, and Indo-European languages. More recent proponents of the Kurgan hypothesis agree that the cultures of Old Europe spoke pre-Indo-European languages but include a less dramatic transition, with a prolonged migration of Proto-Indo-European speakers after Old Europe's collapse due to other factors.