just because someone asked me.
In the USA you cannot practice law across states. You cannot be a plumber, fitter,AC or gas installer, linesman, electrician across states. You cannot be a cab driver across states. Your car insurance is mandatory in some states , not in others

your "registration" must be in the state of residence. Some allow 30 days, some 90. You cannot carry alcohol through some states and even specific counties in some states.
You cannot transport berries, fruits interstate without licences.

The USA is a "country" but it is not a single market. That is why FTA with USA is difficult because states guard their individual laws jealously. "Services" are a nightmare .

The only true single market is the EU and, even in the EU, there are differences in service provision.

In Oz, you can't transport meat or plant products between sates without a vet certificate and some plants are simply banned to transport.

So... the big world that "global britain" needs to understand is that outside EU, the simplest thing is horribly complicated.
Fin

Also. there are city sales taxes (vat) also state taxes and also federal taxes. They differ everywhere. The corporate tax rate is 1 or 2% in Delaware and up to 35% in California BUT it depends on the product or service.

I should finish this thread.
UK can open its NHS to drug purchasing "level playing field " with USA but, that is ONE way as various states will always restrict their purchasing as decided by their state legislature.

Covid has shown that USA states compete for medical devices and medicines. They bid against eachother and the result is messy.

EU members chose to avoid that, paid less. It slowed things down probably because ( big surprise) pharma companies prefer states and countries bidding UP their profit.