Final answer:
China is the country where communism was successfully established under Mao Zedong's leadership after the Chinese Civil War, resulting in the founding of the People's Republic of China in 1949. Option a is the correct answer.
Step-by-step explanation:
The country that saw the successful establishment of communism under the leadership of Mao Zedong is China. This occurred after a prolonged civil war following World War II, where Mao's Chinese Communist Party (CCP) overthrew the Nationalist government.
Mao Zedong's approach to communism was distinct in that he believed the Chinese peasantry were the key to revolution, a perspective that diverged from classical Marxism, which emphasized the industrial proletariat as the revolutionary class. Under Mao's leadership, the People's Republic of China was founded in 1949, and it remained a staunchly communist nation aligning initially with the Soviet Union during the early years of the Cold War.