<P> A declaration of war is a formal act by which one state goes to war against another . The declaration is a performative speech act (or the signing of a document) by an authorized party of a national government, in order to create a state of war between two or more states . </P> <P> The legality of who is competent to declare war varies between nations and forms of government . In many nations, that power is given to the head of state or sovereign . In other cases, something short of a full declaration of war, such as a letter of marque or a covert operation, may authorise war - like acts by privateers or mercenaries . The official international protocol for declaring war was defined in the Hague Convention (III) of 1907 on the Opening of Hostilities . </P> <P> Since 1945, developments in international law such as the United Nations Charter, which prohibits both the threat and the use of force in international conflicts, have made declarations of war largely obsolete in international relations . In addition to this, non-state or terrorist organizations may claim to or be described as "declaring war" when engaging in violent acts . These declarations may have no legal standing in themselves, but they may still act as a call to arms for supporters of these organizations . </P>

Who has the authority to declare war on another country
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