Casus belli -- event used to justify starting a war

from www.wordsmith.org

From Seymour Hersh's story "Preparing the Battlefield" in the July 7-14 New Yorker:
"The public had supported the idea of retaliation, and was even asking why the U.S. didn’t do more. The former official said that, a few weeks later, a meeting took place in the Vice-President’s office. 'The subject was how to create a casus belli between Tehran and Washington,' he said."

casus belli (KAY-suhs BEL-i, rhymes with bell-eye, BEL-ee) noun
An action or event that causes or is used to justify starting a war.
[From New Latin casus belli, from Latin casus (occasion), belli, genitive of bellum (war).]

"Education, both secondary and tertiary, remains a battleground, though the casus belli seems to be more about funding than egalitarianism."
-- Stan Heyl; Class War - The Struggle Goes On; The Independent (London, UK); May 19, 2001.