
I mean in a way landtrust isn’t entirely wrong? In the past, open borders was enabled by two things: the difficulty of long distance travel, and many immigration destinations being settler states who wanted immigrants to fill frontier lands. People moved, but it’s so much easier and affordable now than it once was.
It was a much slower process at the time sure, less people could decide to pack up and move across the world. But it was still incredibly common. Like Celtic peoples were a majority in Western Europe, before being driven to just the British isles. Finns and Hungarians came from eastern Russia. Russia became controlled by the Norse, Bulgaria by Turkic peoples, the pacific was mostly colonized by Polynesians/Melanesians by hopping from island to island.