What's a "War"?

Mark Tushnet

What we need to know is what constitutes a “War” within the meaning of the “declare War” clause. In the framing era what distinguished “wars” from other forms of international interactions was the jus ad bellum. And, under that law, the distinguishing characteristic of a “war” was that it opened up the nation to lawful retaliation, giving the target nation a lawful privilege to kill U.S. soldiers. The Security Council’s resolution means that Libya cannot lawfully – that is, within the bounds of the jus ad bellum – retaliate against those who use force against it. It follows that the U.S. action is not a “War” within the meaning of the “declare War” clause. (Note that there might be a functional justification for this international-law oriented definition of “War” for domestic constitutional purposes: Lawful retaliation, including the privilege to kill U.S. soldiers, is probably the most serious kind of interaction that a U.S. action can open the nation to, so requiring congressional involvement makes functional sense. But my argument doesn’t rely heavily on the functional argument.)

The key point in this argument is that a Security Council resolution authorizing the use of force deprives the target nation of the right to retaliate. I can't cite sources saying that, but it seems to me a sensible construction of the relation between the UN's regulation of the use of force in international relations and the jus ad bellum. A couple of implications of this line of argument should be noted. Libya might not be privileged in killing U.S. soldiers, but (or "and") it would still be bound by jus in bellum principles. More important for domestic constitutional purposes, the argument implies that a Security Council resolution authorizing the use of force relieves a U.S. President of any obligation to obtain congressional authorization for actions taken pursuant to such a resolution. So, for example, the first President Bush would not have needed, as a constitutional matter, congressional authorization to use U.S. forces in the operation aimed at expelling Iraq from Kuwait.