Obviously the civil-war tag should not mean any particular civil war since in the main every country will use the term "the civil war" to mean its own civil war. Even Americans must know that their civil war isn't the only civil war referred to by English language speakers. So spanish-civil-war is the correct tag for the Spanish Civil War, american-civil-war for the American Civil War, english-civil-war for the English etc.
But I did think at the time those questions appeared that it was valid as a tag in its own right because civil wars as a group might be interesting.
But thinking again, it's probably redundant, and anyone interested in civil wars as a phenomena can easily search
The only reason to keep it is if there are conflicts which aren't commonly referred to as civil wars or "the X civil war", such as the Northern Ireland conflict or the war in Bosnia. Questions about these conflicts might not otherwise have "civil war" in their title, body or tag system but it might be interesting to tag them as civil wars.