NATO (North Atlantic Treaty Organization) was formally established as a military alliance in 1949. The founding treaty, signed on April 4 in Washington, D.C., created a system of collective defense whereby member states would respond collectively to an attack against any one of them. This marked a significant response to post-World War II tensions, particularly the threat posed by the Soviet Union during the onset of the Cold War. NATO aimed to promote military cooperation, deter aggression, and maintain peace in the North Atlantic region, solidifying Western alliances against potential communist expansion in Europe.