International law as a legal system differs from domestic legal systems. International law derives its basis primarily from state practice and state consent represented in the form of treaties, custom or general principles of law acknowledged by all states or by all principal legal systems. This law can usually be changed by international agreement. Unfortunately, there is no central enforcement authority equipped to resolve disputes similar to the domestic enforcement mechanisms of states. Consequently, if one nation breaks the rules, it is only correctable by coercive pressure from other states.

Regardless intentions legal-political processes through diplomatic methods might and can escalate to the use of force against the territorial integrity or political independence of any state. This military necessity is armed conflict regardless of the lack of formal declarations of war. War became a politically incorrect term after World War II and the term "armed conflict" is now the preferred term for armed hostilities between states. Consequently, the element of international law governing the relationship between states during armed hostilities is known as the Law of Armed Conflict.

At some point, International law began to include the principal that the means to achieve military victory are not unlimited and that it is bounded by principles of humanity which forbids the infliction of suffering, injury or destruction not actually necessary for the accomplishment of legitimate military purposes. The law of war is to be found not only in treaties, but also in the customs and practices of States, which gradually obtained universal recognition, and form the general principles applied by jurists and practiced by military courts.

The United States of America has always viewed the law of armed conflict as important. Generally, the law of armed conflict represents the fundamental legal basis behind rules of engagement. Rules of engagement are the instructions the United States issues to its armed forces for the purposes of conducting military operations against other states. The Law of armed conflict is used in addition to the Uniform Code of Military Justice by the United States of America to enforce certain obligations of conduct and behavior on individual members of its Armed Forces.

The Law of armed conflict neither authorizes nor prohibits the basic decision to use force. It exists independently of the causes of the conflict and applies regardless of the causes if there is in fact an international armed conflict. The law of armed conflict does not generally apply to conflicts occurring solely within the territory of a state between persons who are nationals of that state. However, insurgents and the state's armed forces in internal disputes are generally coerced by the international community to abide by the law of armed conflict when there is a general civil war involving sustained armed conflict and the insurgents control a significant portion of national territory.