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, torturing, destroying civilian property, taking hostages, performing a perfidy, raping, using child soldiers, pillaging, declaring that no quarter will be given, and seriously violating the principles of distinction and proportionality, and military necessity.
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.
The trial of Peter von Hagenbach by an ad hoc tribunal of the Holy Roman Empire in 1474 was the first "international" war crimes trial, and also of command responsibility. He was convicted and beheaded for crimes that "he as a knight was deemed to have a duty to prevent", although he had argued that he was "just following orders".
In 1865, Henry Wirz, a Confederate States Army officer, was held accountable by a military tribunal and hanged for the appalling conditions at Andersonville Prison, where many Union prisoners of war died during the American Civil War.
The Hague Conventions were international treaties negotiated at the First and Second Peace Conferences at The Hague, Netherlands, in 1899 and 1907, respectively, and were, along with the Geneva Conventions, among the first formal statements of the laws of war and war crimes in the nascent body of secular international law.
The Geneva Conventions are four related treaties adopted and continuously expanded from 1864 to 1949 that represent a legal basis and framework for the conduct of war under international law. Every single member state of the United Nations has currently ratified the conventions, which are universally accepted as customary international law, applicable to every situation of armed conflict in the world. However, the Additional Protocols to the Geneva Conventions adopted in 1977 containing the most pertinent, detailed and comprehensive protections of international humanitarian law for persons and objects in modern warfare are still not ratified by a number of States continuously engaged in armed conflicts, namely the United States, Israel, India, Pakistan, Iraq, Iran, and others. Accordingly, states retain different codes and values with regard to wartime conduct. Some signatories have routinely violated the Geneva Conventions in a way which either uses the ambiguities of law or political maneuvering to sidestep the laws' formalities and principles.
Three conventions were revised and expanded with the fourth one added in 1949:
Two Additional Protocols were adopted in 1977 with the third one added in 2005, completing and updating the Geneva Conventions:
A small number of German military personnel of the First World War were tried in 1921 by the German Supreme Court for alleged war crimes.
The modern concept of war crime was further developed under the auspices of the Nuremberg Trials based on the definition in the London Charter that was published on August 8, 1945. (Also see Nuremberg Principles.) Along with war crimes the charter also defined crimes against peace and crimes against humanity, which are often committed during wars and in concert with war crimes.
Also known as the Tokyo Trial, the Tokyo War Crimes Tribunal or simply as the Tribunal, it was convened on May 3, 1946 to try the leaders of the Empire of Japan for three types of crimes: "Class A" (crimes against peace), "Class B" (war crimes), and "Class C" (crimes against humanity), committed during World War II.
On July 1, 2002, the International Criminal Court, a treaty-based court located in The Hague, came into being for the prosecution of war crimes committed on or after that date. Several nations, most notably the United States, China, Russia, and Israel, have criticized the court. The United States still participates as an observer. Article 12 of the Rome Statute provides jurisdiction over the citizens of non-contracting states in the event that they are accused of committing crimes in the territory of one of the state parties.
War crimes are defined in the statute that established the International Criminal Court, which includes:
However the court only has jurisdiction over these crimes where they are "part of a plan or policy or as part of a large-scale commission of such crimes".
The Saudi Arabian-led military intervention in Yemen has been dubbed as the world's worst humanitarian crisis by the United Nations. The war of more than four years has led Yemen to the brink of extinction with millions of civilians facing famine and starvation at the hands of multiple warring parties; Houthi rebels, Saudi Arabia, and the United Arab Emirates. A December 2019 report by the Amnesty International followed six months of research and documented the lack of medical attention and neglect faced by more than 4.5 million Yemenis, disabled in the war.
War crimes are serious violations of the rules of customary and treaty law concerning international humanitarian law that have become accepted as criminal offenses for which there is individual responsibility. Colloquial definitions of war crime include violations of established protections of the laws of war, but also include failures to adhere to norms of procedure and rules of battle, such as attacking those displaying a peaceful flag of truce, or using that same flag as a ruse to mount an attack on enemy troops. The use of chemical and biological weapons in warfare are also prohibited by numerous chemical arms control agreements and the Biological Weapons Convention. Wearing enemy uniforms or civilian clothes to infiltrate enemy lines for espionage or sabotage missions is a legitimate ruse of war, though fighting in combat or assassinating individuals behind enemy lines while so disguised is not, as it constitutes unlawful perfidy. Attacking enemy troops while they are being deployed by way of a parachute is not a war crime. However, Protocol I, Article 42 of the Geneva Conventions explicitly forbids attacking parachutists who eject from disabled aircraft and surrendering parachutists once landed. Article 30 of the 1907 Hague Convention IV - The Laws and Customs of War on Land explicitly prohibits belligerents to punish enemy spies without previous trial.
War crimes also include such acts as mistreatment of prisoners of war or civilians. War crimes are sometimes part of instances of mass murder and genocide though these crimes are more broadly covered under international humanitarian law described as crimes against humanity. In 2008, the U.N. Security Council adopted Resolution 1820, which noted that "rape and other forms of sexual violence can constitute war crimes, crimes against humanity or a constitutive act with respect to genocide"; see also war rape. In 2016, the International Criminal Court convicted someone of sexual violence for the first time; specifically, they added rape to a war crimes conviction of Congo Vice President Jean-Pierre Bemba Gombo.
War crimes also included deliberate attacks on citizens and property of neutral states, such as the Japanese attack on Pearl Harbor. As the attack on Pearl Harbor happened while the U.S. and Japan were at peace and without a just cause for self-defense, the attack was declared by the Tokyo Trials to go beyond justification of military necessity and therefore constituted a war crime.
War crimes are significant in international humanitarian law because it is an area where international tribunals such as the Nuremberg Trials and Tokyo Trials have been convened. Recent examples are the International Criminal Tribunal for the Former Yugoslavia and the International Criminal Tribunal for Rwanda, which were established by the UN Security Council acting under Chapter VIII of the UN Charter.
Under the Nuremberg Principles, war crimes are different from crimes against peace. Crimes against peace include planning, preparing, initiating, or waging a war of aggression, or a war in violation of international treaties, agreements, or assurances. Because the definition of a state of "war" may be debated, the term "war crime" itself has seen different usage under different systems of international and military law. It has some degree of application outside of what some may consider to be a state of "war", but in areas where conflicts persist enough to constitute social instability.
The legalities of war have sometimes been accused of containing favoritism toward the winners ("Victor's justice"), as some controversies have not been ruled as war crimes. Some examples include the Allies' destruction of Axis cities during World War II, such as the firebombing of Dresden, the Operation Meetinghouse raid on Tokyo (the most destructive single bombing raid in history), and the atomic bombings of Hiroshima and Nagasaki. In regard to the strategic bombing during World War II, there was no international treaty or instrument protecting a civilian population specifically from attack by aircraft, therefore the aerial attacks on civilians were not officially war crimes. The Allies at the trials in Nuremberg and Tokyo never prosecuted the Germans, including Luftwaffe commander-in-chief Hermann Göring, for the bombing raids on Warsaw, Rotterdam, and British cities during the Blitz as well as the indiscriminate attacks on Allied cities with V-1 flying bombs and V-2 rockets, nor the Japanese for the aerial attacks on crowded Chinese cities. Although there are no treaties specific to aerial warfare, Protocol 1, Article 51 of the Geneva Conventions explicitly prohibits the bombardment of cities where civilian population might be concentrated regardless of any method. (see Aerial bombardment and international law).
Controversy arose when the Allies re-designated German POWs (under the protection of the 1929 Geneva Convention on Prisoners of War) as Disarmed Enemy Forces (allegedly unprotected by the 1929 Geneva Convention on Prisoners of War), many of which then were used for forced labor such as clearing minefields. By December 1945, six months after the war had ended, it was estimated by French authorities that 2,000 German prisoners were still being killed or maimed each month in mine-clearing accidents. The wording of the 1949 Third Geneva Convention was intentionally altered from that of the 1929 convention so that soldiers who "fall into the power" following surrender or mass capitulation of an enemy are now protected as well as those taken prisoner in the course of fighting.
Under the Law of Armed Conflict (LOAC), the death of non-combatants isn't necessarily a violation, there are many things to take into account. Civilians cannot be made the object of an attack, but the death/injury of civilians while conducting an attack on a military objective are governed under principles such as of proportionality and military necessity and can be permissible. Military necessity "permits the destruction of life of ... persons whose destruction is incidentally unavoidable by the armed conflicts of the war; ... it does not permit the killing of innocent inhabitants for purposes of revenge or the satisfaction of a lust to kill. The destruction of property to be lawful must be imperatively demanded by the necessities of war"
For example, conducting an operation on ammunition depot or a terrorist training camp would not be prohibited because a farmer is plowing a field in the area, the farmer is not the object of attack and the operations would adhere to proportionality and military necessity. On the other hand, an extraordinary military advantage would be necessary to justify an operation posing risks of collateral death or injury to thousands of civilians. In "grayer cases" the legal question of whether the expected incidental harm is excessive may be very subjective. For this reason, States have chosen to apply a "clearly excessive" standard for determining whether a criminal violation has occurred.
When there is no justification for military action, such as civilians being made the object of attack, a proportionality analysis is unnecessary to conclude that the attack is unlawful.
For aerial strikes, pilots generally have to rely on information supplied external sources (Headquarters, ground troops) that a specific position is in fact a military target. In the case of former Yugoslavia, NATO pilots hit a civilian object (United States bombing of the Chinese embassy in Belgrade) that was of no military significance, but the pilots had no idea of determining it aside from their orders. The committee ruled that "the aircrew involved in the attack should not be assigned any responsibility for the fact they were given the wrong target and that it is inappropriate to attempt to assign criminal responsibility for the incident to senior leaders because they were provided with wrong information by officials of another agency.". The report also notes that "Much of the material submitted to the OTP consisted of reports that civilians had been killed, often inviting the conclusion to be drawn that crimes had therefore been committed. Collateral casualties to civilians and collateral damage to civilian objects can occur for a variety of reasons." 
The Rendulic Rule is a standard by which commanders are judged.
German General Lothar Rendulic was charged for ordering extensive destruction of civilian buildings and lands while retreating a suspected enemy attack in what is called scorched earth policy for the military purpose of denying the use of ground for the enemy. He overestimated the perceived risk but argued that Hague IV authorized the destruction because if it's necessary to war. He was acquitted of that charge.
Under the "Rendulic Rule" persons must assess the military necessity of an action based on the information available to them at that time; they cannot be judged based on information that subsequently comes to light.