An act or situation provoking or justifying war. The phrase is Latin, and comes from casus 'case', and belli 'of war'; it is recorded in English from the mid 19th century.

What does the phrase casus belli mean?

A casus belli (from Latin: casus belli, 'occasion for war') is an act or event that provokes or is used to justify war. ... It is used retrospectively to describe situations that arose before the term came into wide use, as well as present-day situations, including those in which war has not been formally declared.

How do you use casus belli?

The casus belli was simple, but, as reported, most irritating. If not, although a man of peace, I shall consider it a casus belli! After hundreds of Americans were tragically and suddenly killed, the War Party had its casus belli.