Legal Definitions - casus belli

A casus belli refers to an event, action, or circumstance that serves as a justification or trigger for one nation to declare or engage in war against another. It is the specific reason or provocation cited by a country to legally or morally initiate hostilities.

Here are some examples to illustrate this concept:

• Direct Military Aggression: Imagine Country A launches a surprise missile strike that destroys a significant naval fleet belonging to Country B, stationed in international waters. Country B would likely declare this unprovoked attack a casus belli, presenting it as the direct justification for initiating a military response to defend its assets and sovereignty.

• State-Sponsored Terrorism: Suppose intelligence agencies gather irrefutable evidence that Country X secretly funded and organized a major terrorist attack that killed hundreds of Country Y's citizens in a foreign capital. Country Y could then declare this state-sponsored act of terrorism a casus belli, arguing that it constitutes an act of war requiring a retaliatory response to protect its people and national interests.

• Violation of Critical International Treaty: Consider a scenario where two nations, Alpha and Beta, have a long-standing treaty guaranteeing Beta's unrestricted access to a vital river for trade and water supply. Country Alpha suddenly constructs a massive dam upstream, diverting the river's flow and severely impacting Beta's economy and agricultural capacity, in direct violation of the treaty. Country Beta could present Alpha's action as a casus belli, arguing that the violation of such a critical treaty, which threatens its national survival, justifies military intervention to restore its rights and security.