Final answer:
The United States and the Soviet Union were the two major superpowers at odds during the Cold War, engaging in an ideological and political rivalry without direct military conflict due to the threat of Mutually Assured Destruction.
Step-by-step explanation:
The two major superpowers at odds during the Cold War were the United States and the Soviet Union. This period began shortly after the end of World War II, extending roughly from 1945 until the collapse of the USSR in 1991. The Cold War was characterized by a rivalry that never escalated into a full-scale 'hot' war, largely due to the knowledge that such conflict could lead to Mutually Assured Destruction (M.A.D.) because both nations had amassed large nuclear arsenals. Instead, they engaged in various forms of indirect competition, including an arms race, technological and scientific rivalry, such as the space race, and influencing third-party conflicts known as 'proxy wars' like those in Vietnam and Korea.
The ideological battle, with the US promoting capitalism and democracy, and the USSR advocating for communism, spilled into all aspects of global politics and social life. Although the Potsdam Conference saw a brief moment of cooperation, it soon descended into suspicions and the struggle for technological, military, and political supremacy guided the foreign policies of both superpowers throughout the Cold War era.