casus belli

plural casus bellis

1. An act seen as justifying or causing a war; an act of war.

   In ancient times, repeatedly failing to pay tribute by a vassal state was often used as a casus belli by the patron.

   5 more examples

   The Executive, however, can do many acts which would constitute a casus belli, and thus indirectly result in war; but this does not imply in the Executive a concurrent power to declare war, and the war which would result would be one declared by a foreign power.

   1897, Congressional Record, U.S. Government Printing Office, page 664

   Algiers seethed, and this was the casus belli for the ‘ultras’ to attempt a general strike.

   1977, Alistair Horne, A Savage War of Peace, New York: Review Books, published 2006, page 309

   Furthermore, if the French had airily waved away one potential casus belli, more than enough causes of potential conflict remained embedded in the Aix-la-Chapelle Treaty.

   2002, Colin Jones, The Great Nation, Penguin, published 2003, page 138

   Had Saddam taken only the Rumaila oil field and the Bubiyan and Warba islands, there would have been no casus belli.

   2010, Christopher Hitchens, Hitch-22, Atlantic, published 2011, page 290

   And Washington needs to communicate clearly with not only its allies but also the American public on the risks involved if spillover from Ukraine into Article 5 territory verges on a casus belli — an event that provokes a war.

   2022 March 1, Mary Elise Sarotte, “I’m a Cold War Historian. We’re in a Frightening New Era.”, in The New York Times, →ISSN