no the difference is the US was started as a union from the get go, it was founded that way. the US has a constitution which supposedly recognizes certain inalienable rights
the EU tried to usurp member nations by secret legislation and backhanded deals over the course of 50 years till people suddenly woke up and the EU finally admitted, ya we been lying to you for 50 years, now your in the EU, hope your constitutions didnt give you too many freedoms before cause now you can kiss them goodbye