Cities had guards. There was no border pre-1900 because there was no tech to enforce it. If you moved from one place to another, you were mostly at the whims of thieves and pirates.
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.
Nothing in the comment that we are talking about indicates that "pre-1900" is referring to 1900 BCE. It sounds squarely like it's referring to 1900 AD to me. Which is why people are saying it's ridiculous.
> It sounds squarely like it's referring to 1900 AD to me.
What part of "If you moved from one place to another, you were mostly at the whims of thieves and pirates." suggests 1900 CE to you? Have you never looked at a history book?
There are still plenty of pirates around to this very day; a "significant issue" according to your own link. Despite that, the aforementioned statement doesn't make me think it has anything to do with today. What, specifically, makes you think it has something to do with the time leading up to 1900 CE rather than 1900 BCE?