Final answer:
China became a communist nation in 1949 when Mao Zedong declared the establishment of the People's Republic of China on October 1st after the Chinese Communist Party defeated the Nationalist forces.
Step-by-step explanation:
In 1949, China went through a profound transformation that shifted its political landscape dramatically. On October 1, 1949, after a prolonged civil war that resumed after World War II, Communist leader Mao Zedong proclaimed the establishment of the People's Republic of China (PRC) in a grand ceremony held at Tiananmen Square in Beijing. This marked the victory of the Communist Party over the Nationalist forces, who retreated to Taiwan which continued to be recognized as the official government of China by the United Nations until 1971 due to the Cold War politics.
The Communist victory was a culmination of a decades-long struggle between the Nationalist Party (GMD) headed by Chiang Kai-shek and the Chinese Communist Party (CCP) led by Mao Zedong. Following the defeat of Japan in World War II, the tenuous cooperation between the GMD and CCP gave way to full-blown civil conflict, with the CCP emerging victorious. This established the communist state and ended the Nationalists' rule on mainland China.
After the proclamation of the PRC, Mao promised widespread reforms and development, including industrialization, land reforms for peasants, and civil liberties, which marked the beginning of a new era in Chinese history and a significant shift in the global balance of power due to the spread of communism.