Roman philosopher and statesman Seneca (c. 3 B.C.E.–C.E. 65) said that law fell silent during war, but, this is far from the case. Norms regulating behavior in war were the mark of many ancient civilizations. From ancient times to the medieval laws of chivalry, limitations have been imposed in the name of humanity and commonsense on warfare. In the twenty-first century, the laws of war are voluminous and often effective.

These laws are found in treaties such as the four Geneva Conventions of 1949 and the two Additional Protocols of 1977, in the custom and practice of nations, and in the decisions of various international tribunals such as the International Criminal Tribunal for the Former Yugoslavia (ICTY). Military training, in the West at least, almost always includes sessions on the laws of war and the appropriate conduct of hostilities. Lawyers now play a relatively prominent role...