The laws of war shape but do not determine how states fight. States have created these laws to limit the violence and destruction of war, but those efforts face the reality of the strategic incentives of states and soldiers at war. Not all states see the limits of the laws of war as in their interest during war; not all soldiers will follow those rules, even in the best-disciplined armies. Even those who wish to follow the rules may breach them to protect themselves. An effective legal system to limit violence during war must adapt itself to the strategic logics of war and combat. Such a system can shape how states and their militaries act during war by creating shared expectations about what acts are inappropriate conduct and what are proper responses to such conduct. Treaty law creates both a universal standard and the means for public acceptance of that standard. Rejection of a treaty standard signals the desire for an unrestrained battlefield and the likelihood of state policy to create one should war come. Treaty law aids the parties in resolving the uncertainty created by different views of appropriate conduct among states and different willingness to follow any rules among soldiers on the battlefield. Joint ratification entails the belief that both sides will seek to control their own soldiers’ behaviors through training and discipline. It also creates strategic expectations of restraint between soldiers of the warring sides. Despite its failures, the law of war has restrained the destruction of war.

The successes and failures of the laws of war arise from differences in wars and the issues faced. Joint ratification leads to more restraint and stronger reciprocal responses when restraint fails. Democracies are more restrained, except when they are not legally bound either through the absence of a treaty, the failure to ratify one, a lack of clarity in what restraint means, or an issue in which noise overwhelms any effort to comply. Autocracies can only be restrained by the threat of retaliation, and unfortunately they do not often fear that retaliation (and they may even welcome it). Unilateral restraint can weaken deterrence through reciprocity. Those issues in which control of violations can be held closely by military authorities have less noise and better records of restraint; those in which every soldier possesses the power to violate have the worst records of compliance.