belligerency (bəlĭjˈərənsē) [key], in international law, status of parties legally at war. Belligerency exists in a war between nations or in a civil war if the established government treats the insurgent force as if it were a sovereign power. The rules of international law as formulated at the Hague Conferences require that belligerency between states be preceded by an absolute declaration of war or an ultimatum prescribing the terms on which the issuing power will refrain from war. When belligerency has been established, the relations between the warring powers are determined by the laws of war (see war, laws of). In civil wars if the insurgent force is granted belligerency rights, neutral nations generally abstain from supplying or helping either the established government or its opponent. An example of this practice is found in the neutrality proclamations issued by European powers in the American Civil War. Neutral nations may refuse to recognize the belligerency of an insurgent, however, and in this way preserve the right to claim any damages that accrue against the established government for having failed to suppress the rebellion without delay. Under its charter, the United Nations recognizes as legitimate only wars that are fought in self-defense, or for the collective enforcement of the UN Charter. All other wars are regarded as illegal acts of aggression. The United Nations also considers civil wars as threatening to international peace, and, when possible, takes measures to end such hostilities (e.g., Kashmir, Palestine, Korea, the Congo, Cyprus).
See W. L. Gould, An Introduction to International Law (1957).