What are agreements between countries for mutual defense called?

Agreements between countries for mutual defense are known as alliances. An alliance is a formal agreement between two or more nations to cooperate for specific purposes, often related to defense and security. These arrangements can involve military support in the event one of the countries is attacked. Historical examples include NATO (North Atlantic Treaty Organization), which was created to provide collective defense against aggression.

While coalitions can refer to temporary alliances formed for a specific purpose, they are often more associated with political or military campaigns rather than long-term defense commitments. Pacts and treaties can cover a range of agreements, including those related to trade or peace, but the term that specifically pertains to mutual defense is alliances. Therefore, in the context of mutual defense agreements, alliances are the most fitting term.