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.

>after dismantling their own manufacturing

Uhm, Europe is not the US. We still have a lot of manufacturing. It varies by country - the UK unfortunately had structural problems, finance supremacy and a Thatcher who hated unions so much that she'd rather destroy unionized industries than have unions. Central Europe still does a pretty large amount of manufacturing.