When 2 or more country have an agreement that they will protect each other if attacked?

When two or more countries have an agreement to protect each other if attacked, it is known as a mutual defense treaty. Such agreements are designed to deter aggression by promising military support in the event of an armed attack against one of the signatory nations. Examples include NATO (North Atlantic Treaty Organization), where member states commit to collective defense. These treaties can enhance security and stability among allied nations while often influencing international relations and geopolitical dynamics.