War crimes is an interesting thing, cause everyone knows what it kinda is, everyone goes oh yeah the nazis did bad thing, but few understand what they actually are.

[The Hauge] (https://archive.org/details/hagueconventions00inteuoft) conventions of 1899 and 1907 and the Geneva conventions are the first examples of international law outlying the so called 'rules of war'. The 1899 Hauge convention States that countries must Adhere to the geneva convention's treatment of the wounded and made illegal the use of poisons, the exacution of enemy soldiers who have surrendered , looting of a town or place, the attack of undefended towns or the people living there and forcing people to fight against there own people.

It wasent untill 1945 that these laws where probably used to try war criminals, however it wasent the first time people tried. At the end of world war 1 that allies attempted to try 900 Germans for war crimes, however only 15 where successful brought to trial, and where tried in the German court system. However the Nüremberg trials set and international standard in prosecuting war criminals and defined war crimes as in the Nüremberg Charter

A CRIMES AGAINST PEACE: namely, planning, preparation, initiation or waging of a war of aggression, or a war in violation of international treaties, agreements or assurances, or participation in a common plan or conspiracy for the accomplishment of any of the foregoing;

(b) WAR CRIMES: namely, violations of the laws or customs of war. Such violations shall include, but not be limited to, murder, ill-treatment or deportation to slave labor or for any other purpose of civilian population of or in occupied territory, murder or ill-treatment of prisoners of war or persons on the seas, killing of hostages, plunder of public or private property, wanton destruction of cities, towns or villages, or devastation not justified by military necessity;

(C) CRIMES AGAINST HUMANITY: namely, murder, extermination, enslavement, deportation, and other inhumane acts committed against any civilian population, before or during the war; or persecutions on political, racial or religious grounds in execution of or in connection with any crime within the jurisdiction of the Tribunal, whether or not in violation of the domestic law of the country where perpetrated.<

(Nuremberg Trial Proceedings Vol. 1 Charter of the International Military Tribunal retrieved from http://avalon.law.yale.edu/imt/imtconst.asp)

These principles where used to try nazi war criminals and japenese war criminals in what was a landmark victory for international law.