A mutual-defense treaty is a type of agreement between countries that provides for military assistance or protection in the event of an attack on either country. Synonyms for this term include defense pact, security alliance, collective defense agreement, and mutual security treaty. These agreements are often entered into between neighboring countries or those with shared geopolitical interests and can be critical in maintaining stability and security in a region. The agreements can be bilateral or multilateral, and they are typically negotiated and signed by heads of state or foreign ministers. Some notable mutual-defense treaties include the North Atlantic Treaty Organization (NATO) and the Southeast Asia Treaty Organization (SEATO).