War Crimes:
Even though the prohibition of certain behavior in the conduct of armed conflict can be traced back many centuries, the concept of war crimes developed particularly at the end of the 19th century and beginning of the 20th century, when international humanitarian law, also known as the law of armed conflict, was codified. The Hague Conventions adopted in 1899 and 1907 focus on the prohibition to warring parties to use certain means and methods of warfare. Several other related treaties have been adopted since then. In contrast, the Geneva Convention of 1864 and subsequent Geneva Conventions, notably the four 1949 Geneva Conventions and the two 1977 Additional Protocols, focus on the protection of persons not or no longer taking part in hostilities. Both Hague Law and Geneva Law identify several of the violations of its norms, though not all, as war crimes. However there is no one single document in international law that codifies all war crimes. Lists of war crimes can be found in both international humanitarian law and international criminal law treaties, as well as in international customary law.
The 1949 Geneva Conventions have been ratified by all Member States of the United Nations, while the Additional Protocols and other international humanitarian law treaties have not yet reached the same level of acceptance. However, many of the rules contained in these treaties have been considered as part of customary law and, as such, are binding on all States (and other parties to the conflict), whether or not States have ratified the treaties themselves. In addition, many rules of customary international law apply in both international and non-international armed conflict, expanding in this way the protection afforded in non-international armed conflicts, which are regulated only by common article 3 of the four Geneva Conventions and Additional Protocol II.