Final answer:
The Sino-Japanese War occurred last in the series of events in modern Chinese history.
Step-by-step explanation:
The correct answer is Option 4: The Sino-Japanese War. The Sino-Japanese War occurred last in the series of events mentioned in modern Chinese history. The war took place from 1937 to 1945 and was fought between China and Japan. It ended with the victory of the Communist leader Mao Zedong in 1949 and the establishment of the People's Republic of China.