Japanese aggression played a significant role in the spread of communism in China. The invasion of China by Japan during the Second Sino-Japanese War (1937-1945) created a power vacuum that allowed the Chinese Communist Party (CCP) to gain strength and support.
The Nationalist government of China, led by Chiang Kai-shek, was weakened by the war with Japan and was unable to effectively resist the CCP's growth. In contrast, the CCP, led by Mao Zedong, presented themselves as a strong and capable resistance force against the Japanese invaders, and gained popular support among the Chinese people.
Furthermore, the CCP benefited from their close cooperation with the Soviet Union, which provided military aid and advisors to the Chinese communists. As a result, the CCP was able to strengthen its military capabilities and organizational structure, which helped them to ultimately defeat the Nationalist forces and establish the People's Republic of China in 1949.
Overall, Japanese aggression contributed to the spread of communism in China by weakening the Nationalist government and creating favorable conditions for the growth and consolidation of the CCP's power.