Augustine and a clear exposition of original sin was in the late 4th-early 5th century, about four hundred years after the Roman Empire had already effectively integrated quite a bit of Europe and Asia into a diverse and sophisticated civilization that wouldn't be seen again for another millenia.

Around six hundred years after Augustine, Europe had William the Conquerer and the Holy Roman Empire, I guess? Five hundred years after that, Europe had the Renaissance based in a reclamation of the heritage of the ancient world.

I don't think original sin did a very good job of achieving the integration of anyone.