The laws of war are effective to the extent that they change how states and their soldiers fight. How the law plays out in practice – that is, how warring parties and their soldiers observe or violate the abstract principles in combat – hinge on the marriage of the abstract principles of the law to the practical situations faced on the battlefield. The practical implications of the abstract principles of that law aid the formation of expectations of conduct on the battlefield. These strategic expectations of how the other side will act shape calculations to observe or violate the law. These shared expectations can create either a battlefield limited by the restrictions of the law or one governed solely by the logic of kill-or-be-killed. Public acceptance of treaties by both sides creates expectations that the limits of the law will be observed by both sides to the best of their abilities. Such expectations may not be realized in practice because of the difficulties of limiting violence during war.

This chapter presents the general norms of the law of war and the strategic problems that make their implementation problematic. These problems occur between states at war and between their soldiers on the battlefield. Even if both warring states desire a limited battlefield, realizing one requires controlling their soldiers so they limit violence. Limiting violence during war at the state level faces the possibility of deliberate violations, opportunistic violations for short-term military advantage, and self-interested interpretations of the law. Soldiers on the battlefield may commit violations on their own initiative against state policy; they may commit inadvertent violations or use perfidy to gain an unfair advantage in combat. Any of these problems can cause the limits of the laws of war to be broken and even to fail completely if the other side retaliates in kind.