Transportion became much cheaper and more efficient, through things like automobiles, large steel ships, and air flight, so people started arriving in larger numbers from further away.

Yes, and the first thing they did was give us the EU and dissolve the internal borders. That's how they roll.
Ethnic property rights are a brake on international communism. And always have been. 

 They didn't desolve the borders and they are still manned within the EU. 

 You said themselves that they are now merely lines on a map. 

 They are arbitrary lines on a map that change many times in history. Some people take meaning from them, others see them for what they are, just lines.