This is something of a random musing, inspired by reading Spanish history and by current events.
We've seen plenty of governments fall over the last century without a foreign invasion. We have also, sadly, seen many instances where a despotic government was able to crush protestors and retain control. What we have not seen is the proliferation of civil wars that seem to occur in many timelines.
So, this is a vague question, but IMO interesting. What turns a revolution into a civil war?