On Earth, in the grand scheme of things, it took a very short time for colonies to a) diverge politically or b) fail. It's not something that stopped happening

On Earth, in the grand scheme of things, it took a very short time for colonies to a) diverge politically or b) fail. It's not something that stopped happening (much) because we became more cuddly. It's just boring old economics. So I think it's unfeasible to maintain a society that rules with an iron fist over interstellar distance and time.