Nope. "But it is not necessary, to constitute war, that both parties should be acknowledged as independent nations or sovereign States. A war may exist where one of the belligerents claims sovereign rights as against the other." Prize Cases, 67 U.S. 635, 666 (1862). "The laws of war, as established among nations, have their foundation in reason, and all tend to mitigate the cruelties and misery produced by the scourge of war. Hence the parties to a civil war usually concede to each other belligerent rights. They exchange prisoners, and adopt the other courtesies and rules common to public or national wars." id. at 667.