There's a huge amount of cross border inter-state migration in the US. Maybe 30% of the population over a lifetime. I would guess less than half of citizens die

There's a huge amount of cross border inter-state migration in the US. Maybe 30% of the population over a lifetime. I would guess less than half of citizens die in the state their parents were born. I echo your amazement with the sheer size of the open border area. It's possibly the largest in the world. US states are very culturally homogenous. Likely the highest similarity in the world among large countries. Possibly a result of such a mixed heritage and extremely pervasive cultural influences. Who really knows though. I've been to many states and the difference between even coasts is the same as maybe 300 miles of travel in Europe or Asia.