casus beli 

A justification of war between one nation and another nation over a valid reason

I have a valid Casus Beli against the nation of Thisisanexampleia, with the reason being that they put pineapple on my pizza

or, in a more serious way,

I declare war on the nation of Ukraine for an armed border conflict that caused ten Russian soldiers on the border to pass away

casus beli by Americaaaaaaaaaaaaaaaaaaaaaaan March 18, 2022