The international humanitarian law has not provided an official (and legally binding definition) of an international armed conflict. Already during the Second World War many military operations were launched without official declaration of the war. The declaration confirmed often the actual situation when both sites were already engaged in military operations. Depart from the concept of war anticipated the actual situation after 1945, when a vast majority of military conflicts were conducted without an official declaration of war.
Based on the jurisprudence and doctrine of ICRC, an international armed conflict exists whenever there is a resort to armed force between States or protracted armed violence between governmental authorities and organized armed groups or between such groups within a State.
The humanitarian law distinguishes three categories of international armed conflicts. Frist, a classical state v. state conflict, second an occupation and third wars of national liberation. In addition, scholars add to this group an “internationalized non-international armed conflict” where an organized armed group fighting against State A, is the agent of State B (which requires to have effective control over that armed group). Wars of national liberation have character of post-colonial conflicts, either against colonial domination, alien occupation or racist regimes. In case of occupation, it does not require armed resistance against occupying forces but just an effective control (partial, total or a de facto control) of a territory of another state.