China's involvement in World War II began with the Second Sino-Japanese War in 1937, later merging with the global conflict after Japan attacked Pearl Harbor. Under both Nationalist and Communist leadership, China resisted Japanese aggression through major battles and guerrilla warfare, enduring significant civilian suffering. Despite internal divisions, China's resistance tied down Japanese forces and contributed to the Allied effort. Following Japan's defeat in 1945, China emerged victorious but war-torn, soon facing a renewed civil war between Nationalists and Communists.