USA is like the European Union.
EU has 28 states: Austria, Belgium, Bulgaria, Croatia, Republic of Cyprus, Czech Republic, Denmark, Estonia..
USA has 50 states: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware...
Well can you get in a car and drive across the eu with out border checks?
Or do you need to show papers to cross from one country to the next?
The USA allows driving from state to state without a border check.
To be frank having lived in the USA for 61 of 63 years it is not very united at the moment.