system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did places like mainland Asia and Europe develop so many unique languages when people were relatively close to each other?
gpt
Close in the modern automobiles and aircraft sense.

But what’s “close” when you’re a medieval peasant who can’t afford a horse?  One day’s walk?  Two?

The pre-industrial world was *much* smaller because everything was limited by the speed of leisurely travel.  You would live and die in a very small radius from where you were born, generation after generation.