Casus belli is a Latin expression generally used to indicate the act or fact which can become cause for a war.
The expression can however be translated in slightly different ways:
- This is the case, the opportunity for a war;
- This is how things go during a war, a typical consequence of war (casus can also mean "accident", "casual event").
Today casus belli is also used to indicate a genre of role-playing games and computer wargames.