“Casus belli” is a Latin term that translates to “cause of war” in English. It refers to a justification or reason that a country or state uses to initiate or justify military conflict or war against another country or state. A casus belli can be a specific event, action, or circumstance that a nation believes is a compelling reason to go to war.
Casus belli refers to a justification for the initiation of war. Some common examples of casus belli include aggression, violation of treaties, territorial disputes, self-defense, and humanitarian intervention. Aggression can be a casus belli when one country invades another’s territory or attacks its forces or citizens. A nation may also use a violation of mutual defense treaties, trade agreements, or other international agreements as a justification for war. Disputes over borders or territory can also lead to a casus belli if diplomatic efforts fail to resolve the issue. A nation may claim that it is acting in self-defense when it perceives a credible threat to its security, which can serve as a casus belli. In some cases, nations may use the need to protect human rights or prevent atrocities as a casus belli for military intervention.
However international law, including the United Nations Charter, governs the use of force between nations and sets out conditions under which military action is lawful. Using a casus belli does not exempt a nation from these legal considerations, and nations are generally expected to seek peaceful means of resolving conflicts before resorting to war.
