The international alliance formed in response to the threat of communism after World War II was the North Atlantic Treaty Organization (NATO), established in 1949. Created as a collective defense arrangement, NATO aimed to counter Soviet expansion in Europe and promote mutual defense among member states. The alliance was based on the principle that an attack against one member would be considered an attack against all. NATO's formation marked a significant shift in global geopolitics, fostering military cooperation among Western nations. It solidified the East-West divide during the Cold War, leading to decades of tension and rivalry between NATO and the Warsaw Pact.