Just war theory
Just war theory was first proposed by Augustine of Hippo, and forms the base for the Laws of Land Warfare, Hague Conventions and the Geneva Conventions, war crimes courts such as the International Military Tribunal (Nuremberg) and the International Criminal Court, and the ethics involved in complex situations such as nuclear deterrence, terrorism, and counterterrorism.
It has three fundamental components:
- jus ad bellum: the justice of going to war
- jus in bello: the means by which war is conducted
- jus post bellum: the means by which the war is concluded and the peace restored
Despite the Latin, the former two terms were articulated in the 20th century. 
That the formal language may be recent does not mean that the ideas are new, or that they are limited to Western societies. Kamehameha I is known for introducing the Law of the Broken Paddle, which reflects the proportionality concept of jus in bello.
- Robert Kolb (31 October 1997), "Origin of the twin terms jus ad bellum/jus in bello", International Review of the Red Cross