Question

how did language spread from one proto-indo-european language to more than 6,000 languages we speak today?

Answer 1

Answer:

We can thank geography for that. If you look at a map of Eurasia, you can see many massive mountain ranges and rivers, all of which separate early tribes apart. When one tribe is split apart for long enough, the people in each tribe develop their own distinct and unique identity, which also includes languages. There are several very interesting researches on this phenomenon online if you look deep enough and I do recommend you check them out, it's quite the fascinating read.