[mr_toad]

> Has there been a regime which has collapsed due to an external strike like this where it hasn't resulted in some decades long civil war nightmare?

People have already mentioned the post WW2 occupation of Germany and Japan.

There’s also the Roman occupation of Greece (and other Hellenistic territories), and even perhaps the Norman occupation of England. Not that either of these didn’t cause some strife and rebellion in both cases, but still there was a concerted effort to build up both territories.