1) Cause of a dispute 2) Event leading to war 3) French monthly magazine 
The term came into wide use in the seventeenth and eighteenth centuries through the writings of Hugo Grotius (1653), Cornelius van Bynkershoek (1707), and Jean-Jacques Burlamaqui (1732), among others, and due to the rise of the political doctrine of jus ad bellum or `just war theory`. The term is also used informally to refer to any `just cause......
Casus belli is the material grounds which justify a declaration of war.
[n] - an event used to justify starting a war
noun an event used to justify starting a war
an event used to justify starting a war