The Evolution of Indo European Languages

A major impetus to borrowing is you have a new technology. And there's some reason to believe some of the spread of Indo European through Western Northern Europe is motivated not by actual Indo European peoples moving, but by technologies of war and agricultural agricultureMoving in particular things like dealing with horses and so forth. The last major thing that sends people flying all over the place is religion. Islam, Christianity, Hinduism, Buddhism, all of these have moved great distance, taking a language and look or at least loan words with them.