A war crime is an act that constitutes a serious violation of the laws of war that gives rise to individual criminal responsibility. Examples of war crimes include intentionally killing civilians or prisoners, torture, destroying civilian property, taking hostages, perfidy, rape, using child soldiers, pillaging, declaring that no quarter will be given, and serious violations of the principles of distinction and proportionality, such as strategic bombing of civilian populations.
The concept of war crimes emerged at the turn of the twentieth century when the body of customary international law applicable to warfare between sovereign states was codified. Such codification occurred at the national level, such as with the publication of the Lieber Code in the United States, and at the international level with the adoption of the treaties during the Hague Conventions of 1899 and 1907. Moreover, trials in national courts during this period further helped clarify the law. Following the end of World War II, major developments in the law occurred. Numerous trials of Axis war criminals established the Nuremberg principles, such as notion that war crimes constituted crimes defined by international law. Additionally, the Geneva Conventions in 1949 defined new war crimes and established that states could exercise universal jurisdiction over such crimes. In the late 20th century and early 21st century, following the creation of several international courts, additional categories of war crimes applicable to armed conflicts other than those between states, such as civil wars, were defined.