What you seem to be missing is that the EU is an organization that legally owes its existence to a series of treaties between 28 sovereign nations and the United States is one, single, sovereign nation under International law. This system of nations is really a post-Napoleon phenomenon and wasn’t solidified until after World War 2. If it had gone a different direction, maybe every American, German, Brazilian and Australian State and every Swiss canton and every Russian oblast would be organized in a manner much like the EU and issue their own passports.

It isn’t a mere organizing principle, there is a legal distinction that is easily drawn with differing legal trappings.

The EU deciding on collective Visa measures is fine, I actually have not taken any issue with that in this entire thread, the only thing I took issue with was a bad analogy which left alone, only confuses and misleads otherwise constructive discussion.

Long and the short of it is: Hawaii and Croatia aren’t analogous to each other vis a vis visa agreements, and that’s because they come from differing International legal positions, a position in which Hawaii is actually irrelevant from beginning to end and Croatia isn’t but has the legal standing and recognition to temporarily be irrelevant in its own visa policies if it chooses to. The nuances are not unimportant.

You are still missing the point that these are fairly arbitrary distinctions. The states of the US are actually quite independent, with much of the authority of the federal government being taken from the 'commerce clause', which is ... er ... "interesting" (and actually not that dissimilar to the EU deriving from the single market and customs union).

Case in point: I have an EU driver's license. It is valid in the EU. When in the US, driver's licenses are per-state, though I am allowed to drive in a different state for a while, I have to get the current state's license when I move my residence. California has border checks for agricultural goods. etc. etc.

These distinctions are only as arbitrary as the law, which can be very arbitrary but ultimately we have agreed to accept the Rule of Law, both my country and most likely yours.

Nations have agreed to fairly consistent diplomatic protocols and channels with which to treat each other. Hawaii can’t issue visas, but Japan can require Americans to apply for a visa. That isn’t just a stretch of the Commerce Clause, it is part of how and why the US Constitution was written the way it was: so individual States weren’t forming international interests contrary to the national interest.

Thank you!! Why does this seem so difficult for some to understand?