Why isn't the American Civil War seen as a war of independence?

So recently, I've been reading lots of books and watching lots of videos about the American civil war as I am very interested in it. But I had a thought that came through my mind, why wasn't the American Civil War seen as a war of independence like the Revolutionary War was? The war was about 11 states declaring independence from a nation and wanting to be its own country, which in a basic definition is a war of independence. I want to make clear I am British and am pretty ignorant about this topic so I would love to hear your opinions!