On (the Law of) War: What Clausewitz Meant to Say
Lepper, Steven J., Air & Space Power Journal
CARL VON CLAUSEWITZ'S theories on military strategy and war have become so ingrained in American military thought that almost every US engagement fought or planned today relies heavily on his concepts. Unfortunately, his most polished writing -the only part of his manuscript he considered ready for publication prior to his untimely death-contains only one specific reference to the law of war: "War is . . . an act of force to compel an enemy to do our will. . . . Attached to force are certain self-imposed, imperceptible limitations hardly worth mentioning, known as international law and custom, but they scarcely weaken it. Force-that is, physical force, for moral force has no existence save as expressed in the state and the law-is thus the means of war; to impose our will on the enemy is its object" (emphasis in original).1 I use the term unfortunately for two reasons. First, this passage suggests that Clausewitz considered international law irrelevant to war.2 Second and more significant, his current-day disciples might infer from it that law is unimportant to the formulation of military strategy and tactics today. This article seeks to refute both inferences. In fact, the opposite is true: the law of war has been, is, and should continue to be a significant factor in the strategic thinking of the US military.
The Law of War Was
(And Clausewitz Knew It)
Students of Clausewitz have often deciphered his cryptic passages by putting them into historical context. That context is also critical to understanding his views on the laws of war. Before Clausewitz, particularly during the seventeenth-century "Wars of Religion," European wars generally were brutal and unrestrained. Since religious and ideological differences motivated combatants, these wars were literally no-holds-barred affairs.
After 1648, when the last of these wars-the Thirty Years' War-ended, Europe entered an age of limited war in which smaller, professional armies fought each other for relatively modest political and territorial objectives.3 Intent on avoiding previous excesses, European sovereigns took steps toward limiting the impact of future conflicts. In addition to establishing formal officer-training courses, they revived chivalry by adopting formal articles of war that imposed strict rules governing treatment of prisoners, noncombatants, and private property. In the early 1800s, Clausewitz attended and taught at the Prussian War College. His cynical reference to the laws of war at least shows that at some point in his career he learned them.
Appreciating Clausewitz's true views on the law of war also requires both a brief reference to Hugo Grotius, the father of modern international law, and an understanding of some of the law's principles and purposes. Grotius, a Dutch lawyer and philosopher, died three years before the end of the Thirty Years' War. His most important work, On the Law of War and Peace, was as influential to the study of international law as Clausewitz's On War was to the study of war.
Grotius articulated fundamental principles that were generally observed in Clausewitz's era and that survive to this day in the forms of military necessity, proportionality, and humanity. All three concepts spring from the basic idea that "the prohibition against intentionally harming other human beings is set aside in warfare only to the extent that combatants of opposing belligerent nations may rightfully attack one another."4 Military necessity permits armed forces to attack only those targets that will impair the enemy's ability to make war. Since attacking noncombatants produces no such impact, this rule also protects them. Proportionality prohibits using force greater than necessary to accomplish legitimate military objectives. Finally, humanity prohibits the infliction of unnecessary suffering. This principle protects combatants from attack with weapons that continue to cause injury after their combatant status ends. …