Cicero said laws are inoperative in war (“silent enim leges inter arma”). In fact, there is U.S. and international law that applies to the decision to use force and the manner and method in which it is used. In U.S. practice there are three contextual legal questions that should arise when the president or his advisors contemplate the use of military force. First, does the president have the constitutional authority to use force? This is a “war powers” question. Second, is the contemplated force lawful under international law? This is a question involving that portion of the law of armed conflict known as the jus ad bellum (thresholds for resorting to force). Third, are the means selected lawful? This is a question involving the jus in bello (the law applying to the means and methods of war). It may also be a question of U.S. criminal law to the extent that U.S. law implements international law, or imposes obligations independent of international law.

Few areas of law are as important to national security as is this collective body of domestic and international law. This is intuitive in situations in which force is actually used; however, in other scenarios falling short of force the implied or express threat of military intervention is itself the catalyst for policy influence. For the national security lawyer, no area of law will have the same implications in defining a world of public order and individual security.