d) NATO

The formation of the North Atlantic Treaty Organization (NATO) in 1949 was a significant event in the post-World War II era, marking a strategic shift in global military alliances. Established with the primary purpose of collective defense, NATO was a direct response to the perceived threat of Soviet aggression in Europe. The alliance, consisting initially of 12 countries including the United States, Canada, and several Western European nations, represented a united front against the spread of communism and Soviet expansion. It served as a cornerstone of U.S. foreign policy during the Cold War, embodying the principle of mutual defense where an attack against one member was considered an attack against all. NATO’s formation played a crucial role in shaping the geopolitical landscape of the 20th century, symbolizing Western solidarity and commitment to collective security.