Final answer:
NATO, or the North Atlantic Treaty Organization, is the military alliance formed by the United States and allies in 1949 to counter Soviet aggression, based on the principle of collective defense.
Step-by-step explanation:
NATO: The Military Alliance for Collective Defense
The military alliance formed by the United States and its allies to provide security in the event of an attack by the USSR is the North Atlantic Treaty Organization (NATO). Founded in April 1949, it originally included the United States, Canada, and ten Western European nations such as Britain and France. Over time, additional countries like Greece, Turkey, and West Germany joined. NATO's core principle of collective defense is encapsulated in Article 5, which states that an armed attack against one member is deemed an attack against all, prompting a unified military response. This alliance served as a counterbalance to the Soviet Union's own military bloc, the Warsaw Pact.
NATO's creation symbolized the end of American isolationism, indicating a commitment to international stability and defense against the perceived threat of communist expansion. Despite being a military organization, NATO's main goals are the peace and stability of Europe rather than territorial expansion. Over the decades, NATO has adapted and expanded beyond its original membership, integrating several Eastern European nations post-Cold War.