The UK however, maybe. Brexit was a real dumb idea.
What in the world are you talking about? The US has all of this internally. If on the one narrow point you want to claim that EU has open-borders to the rest of the world, no you don't and that's not something that's good to have anyways. Both US and European citizens are fighting their own governments to decrease immigration as polling shows large opposition to current immigration levels for many years now. A big part of the crackdown on speech in the UK is to restrict criticism of immigration policy.
A better example would be Americans being able to travel freely to USMCA countries.
It’s (nominally) a union of states after all
The US is over 2 times larger by land.
Population is about a quarter smaller. Still, Massachusetts has more people than Denmark, New York has the same as Romania, California has more people than Poland.
Our original founding documents cite "these united states", interestingly and very tellingly "these", not "the." States are their own entities, and you'd find many to have very different cultures and laws — probably the same level of variance you'd find in the EU.
The rearmament initiative is particularly concerning. Over the past three years, communities in Italy, Spain, Greece, and Germany have been devastated by flooding, wildfires, etc. Rather than prioritizing investment in resilient infrastructure, leaders are channeling resources into rearmament to confront Russia and China (or so they say - since they are acting as clowns anyway no one really pays attention). My concern is that these weapons may ultimately be used by Europeans against one another; It happened twice already.
[^1]: https://www.aa.com.tr/en/europe/temporary-border-controls-to...
[^2]: https://www.politico.eu/article/ursula-von-der-leyen-europe-...
Also, for better or for worse it helps that almost everyone speaks English everywhere.
But European countries are much more different from one another than the States are. I think it's actually quite a challenge to doing business there - growing into another country means you have to appeal to a very different culture, deal with different laws, speak a different language.
The US states have their differences but there's a reason they're part of the same nation.
What usually is that they spend a few hundred millions in consultancy and plans. And then off we go for the next round :-)