Yes and no. These superpowers are playing their power games on a world stage. As such they sometimes need the crowd on their side in order to win. That means that thin veneer of law does indeed count. After all each nation tries to keep their population under the believe that they are indeed the good ones.
That means war cannot move unrestricted from the rules that govern it. Or let's say it can, but at a (often significant) cost.
That means war cannot move unrestricted from the rules that govern it. Or let's say it can, but at a (often significant) cost.