Agriculture, at very least. Before we created that tech you'd be way too busy trying to find something to eat to have time to stand around defending artificial borders. 1900 BCE mightn't be perfectly accurate, but close enough for a stupid comment on the internet.
Agriculture, at very least. Before we created that tech you'd be way too busy trying to find something to eat to have time to stand around defending artificial borders. 1900 BCE mightn't be perfectly accurate, but close enough for a stupid comment on the internet.