European Union construction happened after the second world war in the context of the Marshall Plan ( https://en.wikipedia.org/wiki/Marshall_Plan ) to help rebuild Europe that had been destroyed.

By design European laws are superior to national laws. Leaving the union is also instant bankruptcy because all countries have very high level of debt which are only guaranteed because they are in the union.

European population is getting old and replaced by a migration coming mainly from previous African colonies.

Future paying for the past.