Final answer:
The primary cause of disagreements between Moscow and Beijing in the early 1960s was ideological differences, amidst the global tension of the Cold War.
Step-by-step explanation:
The main reason for serious disagreements between Moscow and Beijing in the early 1960s was B. Ideological differences. During this period, both the Soviet Union and the People's Republic of China were communist states, but they held divergent views on the implementation and direction of communist ideology. This split was also exacerbated by national interests and the pursuit of global influence. While there were underlying territorial and economic tensions, the predominant cause of the Sino-Soviet split was ideological. The Soviet Union, under leaders like Joseph Stalin and Nikita Khrushchev, and China under Mao Zedong had different visions for communism and its role in the world. Their disagreements played out against the backdrop of the Cold War, a time characterized by the competition for global supremacy between the Soviet Union and the United States, which influenced alliances, and economic and military strategies worldwide without direct military confrontation between the superpowers.