What countries entered as a pact to support each other if the event of war?

Countries often enter into military alliances or pacts to support each other in the event of war. Notable examples include NATO (North Atlantic Treaty Organization), established in 1949, which includes the United States, Canada, and several European nations. Another example is the Warsaw Pact, formed in 1955 as a collective defense treaty among Soviet-aligned countries during the Cold War. Additionally, modern alliances like AUKUS (Australia, the UK, and the US) and security agreements in the Indo-Pacific region serve similar purposes today.