At that time, Mao Zedong was a young communist revolutionary who had recently returned to China from France. He and his fellow communists were initially supportive of the Nationalist government, but they soon became disillusioned with its policies.
In 1927, the Nationalists launched a massacre of communists in Shanghai, known as the Shanghai Massacre. This event marked the beginning of the Chinese Civil War, which would last for over two decades.
During the Chinese Civil War, Mao and his communist supporters fought against the Nationalist government. In 1949, the communists finally won the war, and Mao became the leader of the People's Republic of China.