For the purposes of this chapter, war with a foreign power exists under any of the following conditions:
(a) Whenever Congress has declared war and peace has not been formally restored.
(b) Whenever the United States is engaged in active military operations against any foreign power, whether or not war has been formally declared.
(c) Whenever the United States is assisting the United Nations, in actions involving the use of armed force, to maintain or restore international peace and security.