“Is this any sort of official definition? Because I was under the impression that we call some wars civil to distinguish them from foreign wars. The war for independence, for instance, was a civil war from Britain’s perspective. From ours it was foreigners trying to impose their will on us.”
Latter - no. Not foreigners, but sovereigns treating birthright British as mere colonials (i.e., conquered peoples).
A civil war basically is simply in-fighting. In some ways, indeed, it’s hairy calling the “CW” such when basically 1 side just wanted to part ways.
And really, “Revolution” isn’t really good for the British-American war, because THAT absolutely implies someone wants to take over. Perhaps simply because they wanted to “take over” the land they lived on rather than letting far-away kings have ultimate rule.
In any case my take is:
Insurgents win - revolution
Insurgents lose - civil war.
You’re absolutely right in that both the American colonists and the Southern States, or some of them, had declared independence before the wars got into full swing. So according to them they were a foreign nation, and it took the Americans winning to prove it and the Confederates to lose it.
Which isn’t to say what’s civil is always a matter of who you ask, who wins, or it being a fight between two or more factions to control the whole. It can, also, be between a sovereign and lesser internal power for less than independence but more than they have. And probably other scenarios I can’t think up, too.