NATO (1949)
To counter Soviet expansionism, the west formed the North Atlantic Treaty Organization. The group's mission was to deter a Soviet strike into Western Europe. Under the NATO Charter, if one nation is attacked, the entire alliance is attacked. The collective defense helped hold the Soviets in check during the Cold War. On October 4, 2001, NATO invoked the charter for the only time in the aftermath of the September 11 attacks on America.