[xyzzyz]

A good mental model is that EU works pretty much like US did 100 years ago. The US states were roughly as sovereign as EU states (with some important differences, especially in defense and immigration), and US federal government was similarly powerful to EU government.

This has, of course, changed over the last century, and US states lost most of their sovereignty. I predict the same will happen to EU states over the next century.

[clarionbell]

That would be in 1920s and states were far from sovereign back then. Maybe 1820s, then one could argue the union was more 'loose'. But even then, the union was pretty tight. Hence constant issue of slavery in federal law.