What did they have that others didn't? The short answer is a lot of people, but China has a lot more, so why didn't they become the main rival of the US?
The Soviet Union was the largest country in the world. Especially after WWII, they were able to influence the whole of Eastern Europe. The expansion meant that they had more people, more resources and were able to draft up trade agreements with Eastern European countries, which brought in avenues and resources. The difference why China did not become a superpower after WWII while the USSR did could be because China was not politically and economically stable after 1945. The Chinese Civil War, and the Cultural Revolution did much damage to Chinese economy and population, leading to economic stagnation. Whereas after WWII, Soviet Union enjoyed peace, and greater political influence, backed by military strength, which put them in a favourable position for growth.
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