Casus Belli 

from Latin: cause for war
a justification or pretext for a declaration of war.

The assassination of Archduke Ferdinand served as a casus belli for the invasion that started World War 1

Casus Belli by Anonymous November 7, 2003

Casus Belli 

1.An act or event that provokes or is used to justify war.
2.A substandarb EQ guild.

1.Iraq going to Kuwait
2.Casus Belli doing Rallos Zek for months on end without success.

Casus Belli by Ogur Bashum July 15, 2003