it appears I’ve opened the floodgates
Let’s accept the premisse: the imperial core has been too strong to allow a revolution. You’d still have to grapple with the fact that the relative power of the imperial core is shrinking in comparison with the rest of the world, which in turn would make it possibel again. (Accept if you’re talking about absolute power instead of relative, but then the amounts of places where it’s possible has been shrinking and there’s probably nowhere left.)