Of course what is meant by being a vassal is up to definition and degree. But a foreign standing army probably is somewhere on that spectrum. Brussels at least

Of course what is meant by being a vassal is up to definition and degree. But a foreign standing army probably is somewhere on that spectrum. Brussels at least has the pretence of the member citizens having (some) democratic control, although I find EU so antidemocratic by design that this is indeed mostly a pretence. And EU e.g. sets quite tight limits of how the member countries can structure their economies.