After World War II, the tension between communist and democratic forms of government strained relations between the Soviet Union and the United States and provided the ideological underpinnings of the Cold War. These tensions almost boiled over into full on conflict several times, especially as nuclear arms proliferation and testing advanced rapidly during the late 1950s and early 1960s. Both nations found it critical to expand their spheres of influence, largely by promoting leadership in the “Third World” that would be sympathetic to their causes.