Casus foederis

Casus foederis(orcasus fœderis) is derived from theLatinfor "case for the alliance". Indiplomaticterms, it describes a situation in which the terms of an alliance come into play, such as one nation being attacked by another.

Historical examples

War of the Pacific

See also:Treaty of Defensive Alliance (Bolivia–Peru)

In theWar of the Pacific,Boliviainvokedcasus foederisto bringPeruinto the war afterChilereinvaded Bolivia's coast. In 1879, Chilean armed forces occupied the port city ofAntofagastaafter Bolivia threatened to confiscate the Chilean Antofagasta Nitrate Company's property. Peru attempted to mediate, but when Bolivia announced that a state of war existed, the situation deteriorated. Bolivia called on Peru to activate their secret mutual defense pact, and Chile demanded for Peru to declare its neutrality immediately. On April 5, Chile declared war on both nations. The following day, Peru responded by acknowledging thecasus foederis.

World War I

InWorld War I,the treaties betweenItalyandAustria-Hungary,andRomania,which purportedly required Italy and Romania to come to Austria's aid if Austria was attacked by another nation, were ignored by both Italy and Romania because, asWinston Churchillwrote, "the casus fœderis had not arisen" since the attacks on Austria had not been "unprovoked."

NATO

Article 5of theNorth Atlantic Treatygoverns mutual defense in the event of an attack on a member nation. It has been invoked only once, on September 12, 2001, in response to theSeptember 11 attacksin theUnited States.

Exceptions

Where a political-military alliance pact is lacking, there is no obligation to intervene militarily alongside those asking for help, as the decision depends exclusively on the discretionary choices of foreign policy of the requested State.

See also

• Casus belli
• List of Latin phrases