Declaration of war
A formal act announcing a state of war between states.
A declaration of war is a formal announcement by one state that it is engaging in or about to engage in war with another. This act, often a speech or the signing of a document by an authorized government official, legally establishes a state of war between nations. The authority to declare war depends on a country’s laws and government structure; in many places, this power rests with the head of state or sovereign. Sometimes, less formal actions—like issuing a letter of marque or conducting a covert operation—can authorize warlike acts by privateers or mercenaries. The Hague Convention (III) relative to the Opening of Hostilities of 1907 set the official international protocol for such declarations.
Since 1945, international law has largely made declarations of war obsolete. The United Nations Charter prohibits both threatening and using force in international conflicts, though declarations may still matter under the domestic laws of warring or neutral nations. The UN Security Council, under Article 42 and Chapter VII of the Charter, can authorize collective action to maintain peace. Article 51 preserves the right to self-defense if an armed attack occurs. Declarations of war have become very rare since World War II. Scholars debate why: some argue states want to avoid international humanitarian law restrictions, while others believe declarations are now seen as aggressive and overly ambitious.
The practice of declaring war is ancient. It appears in the Sumerian *Epic of Gilgamesh* and the Old Testament. The Roman Republic formalized it with the Fetial ritual, though this declined during the Imperial era. Still, declarations were not always used. In his 1883 study *Hostilities without Declaration of War*, British scholar John Frederick Maurice found that between 1700 and 1870, war was declared in only 10 cases (such as France’s 1812 declaration on Russia or British declarations), while 107 wars were fought without one—these figures cover only European and U.S. conflicts, not colonial wars in Africa and Asia.
In modern public international law, a declaration of war recognizes a state of hostilities between countries and regulates military conduct. The Hague Conventions are the key treaties on this. The League of Nations (formed in 1919 after World War I) and the 1928 General Treaty for the Renunciation of War (signed in Paris) showed global efforts to prev
- Definition
- Formal act announcing war by one state against another
- Legal basis
- Hague Convention (III) relative to the Opening of Hostilities
- Decline period
- Since 1945, largely obsolete in international relations
- Key treaty
- United Nations Charter (prohibits threat and use of force)
- Historical rarity
- Between 1700 and 1870, war declared in only 10 of 107 European and US-related cases
- Modern example
- No formal declaration in the Russo-Ukrainian War
Lore & Background
The practice of declaring war has ancient roots, with accounts in the Epic of Gilgamesh and the Old Testament. The Roman Republic formalized it through the ritual of the Fetials, though this declined in the Imperial era. In modern public international law, a declaration of war entails recognition of a state of hostilities and regulates conduct between military engagements, with the Hague Conventions as primary multilateral treaties.
Reader's Guide
Declarations of war have become exceedingly rare since World War II, largely due to developments in international law such as the United Nations Charter, which prohibits the threat and use of force. The UN Security Council may authorize collective action under Chapter VII, and Article 51 preserves the right to self-defense. Scholars debate the causes of the decline: some argue states seek to evade international humanitarian law, while others see declarations as markers of aggression. The Hague Convention (III) of 1907 requires previous explicit warning, either as a reasoned declaration or an ultimatum. Despite their obsolescence in international relations, declarations may still have relevance in domestic law of belligerents or neutral nations.
Did You Know?
- Between 1700 and 1870, war was declared in only 10 of 107 European and US-related cases, according to John Frederick Maurice's study.
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