Restrictions were put in place mostly in the beginning of the century during the WWI. It wasn't "we have trains, let's restrict who can work where" thingy, it w

Restrictions were put in place mostly in the beginning of the century during the WWI. It wasn't "we have trains, let's restrict who can work where" thingy, it was a war thingy. EU was able to abolish those restrictions to great benefit and is trying to make it check-free through the Schengen agreement. It's Romania and Bulgaria who still need to show passports and this creates great friction at the borders but hopefully, this will be no longer the case by the end of the year. In the United STATES of America, people are free to work and travel any any state and notice that people don't simply flock to the richest one. I agree that sudden removal of the borders will create serious issues but this is only because there are borders at first place. The situation will stabilize and you won't see 8B people moving to Canada, 8B people moving to USA, 8B people moving to Germany, 8B people moving to UK.