Definition of casus belli in English:

casus belli

Pronunciation /ˌkɑːsʊs ˈbɛli//ˌkeɪsəs ˈbɛlʌɪ/


  • An act or situation that provokes or justifies a war.

    • ‘Modern wars require a pretext, a casus belli that can be packaged to the public as a sufficient justification for the resort to arms.’
    • ‘The failure to disarm is probably a casus belli.’
    • ‘What was lacking was a suitable pretext, a casus belli.’
    • ‘France countered by getting Russia to propose a general congress, intended to isolate Austria and provoke a casus belli.’
    • ‘The purpose was to provoke a response that could become a casus belli for invasion.’
    • ‘This must be the first example of casus belli (a cause justifying war) being discovered after the war has ended.’
    • ‘This feeling has been particularly pronounced in Poland, which after all had been the casus belli for the Second World War.’
    • ‘He unequivocally presented it as the casus belli.’
    • ‘So we accept that there are legitimate casus belli: acts or situations, ‘provoking or justifying war’.’
    • ‘The assassination of the heir to the throne, Archduke Franz Ferdinand, by a Serbian nationalist was an act of quasi-regicide that no monarchy could regard as other than a casus belli.’
    • ‘It used to be one of those fussy old constitutional conventions that, when a prime minister lied to the nation over something so serious as a casus belli, his resignation was a foregone conclusion.’
    • ‘While retaliatory war relies on the obvious fact of an attack as its casus belli, pre-emptive war opens the door to myriad other justifications.’
    • ‘As the Romans liked a casus belli to justify their aggressive activities, it is not always possible to be certain about the real circumstances behind their intervention.’
    • ‘Neither one of these, do I think, fall into the category that I would describe as threatening enough to be what I would describe as a casus belli.’
    • ‘If a state launched it, it would be an obvious casus belli and the state officers could expect to meet the world's most powerful nation in all-out war.’
    • ‘Various casus belli are served up as conditions change.’
    • ‘It wants a proper casus belli established ahead of the fight.’
    • ‘German violation of the neutrality of Belgium, which since 1839 had been under the protection of the great powers, was for Britain the formal casus belli.’


Latin, from casus (see case) and belli, genitive of bellum ‘war’.


casus belli

/ˌkɑːsʊs ˈbɛli//ˌkeɪsəs ˈbɛlʌɪ/