International humanitarian law is the branch of international law concerned with the waging of warfare. It regulates the conduct of hostilities and the treatment of those not actively participating in the conflict (namely, civilians, the wounded and sick, and prisoners of war). It seeks to minimize suffering and ensure that both combatants and civilians are treated humanely. Although international treaties on the subject are of fairly recent origin, practices regulating armed hostilities are evident throughout history. Even before there were States, battles fought between tribes, clans or other groups were often governed by rules to mitigate the effects of armed violence. The ancient texts of many civilizations show that in war, prisoners were not to be killed but taken and well treated; women, children and the elderly were not to be harmed; and warriors should not use barbarous weapons or methods of attack. While such practices were often founded on grounds of religion, morality or honour, they are the forerunners of the legal regime States have developed to regulate armed conflict.

International humanitarian law is based on the precept that the sole objective of war is to overpower the armed forces of the opponent. Men become the legitimate object of attack solely because of their relationship with the making of warfare. In his renowned work The Social Contract (1762) Jean-Jacques Rousseau formulated one of the law's philosophical footings: