Paul from the Langfocus YouTube channel has made a good video on how the different Indo-European languages are related to each other:
Once more about half of the world population speaks an IE-language. And some scholars believe that this is due to the fact that the speakers of Proto-Indo-European where the first ones to domesticate horses. This enabled them to travel large distances at until then unknown speed and allowed these people spread across a large area, while displacing local languages.
Fascinating Future 