China Declares War on Japan

After the Battle of the Marco Polo Bridge, the Chinese Kuomintang government declared war on the nation of Japan. This military action was the result of Japan’s aggressive expansionist policies.

Summary of Event

The Second Sino-Japanese War (1937-1945) was the result of the political, economic, and geopolitical factors that directed the struggle for control of China in the years following the end of World War I. When the founder of the Chinese Republic, Sun Yixian (also known as Sun Yat-sen), died in 1925, the leadership of the Chinese Kuomintang Party passed into the hands of a young military officer named Chiang Kai-shek. During this period, China was a decentralized state with large regions, especially in the north, which was controlled by independent warlords. Chiang Kai-shek’s Kuomintang Party joined forces with the Chinese Communists led by Mao Zedong and launched a military campaign called the Northern Expedition to reclaim the northeast part of China from the warlords. [kw]China Declares War on Japan (July 7, 1937)
[kw]War on Japan, China Declares (July 7, 1937)
[kw]Japan, China Declares War on (July 7, 1937)
Marco Polo Bridge, Battle of the
China;Second Sino-Japanese War[Second Sinojapanese War]
Japan;Second Sino-Japanese War[Second Sinojapanese War]
Second Sino-Japanese War (1937-1945)[Second Sinojapanese War]
[g]China;July 7, 1937: China Declares War on Japan[09530]
[g]East Asia;July 7, 1937: China Declares War on Japan[09530]
[g]Japan;July 7, 1937: China Declares War on Japan[09530]
[g]Manchuria;July 7, 1937: China Declares War on Japan[09530]
[c]Military history;July 7, 1937: China Declares War on Japan[09530]
[c]Wars, uprisings, and civil unrest;July 7, 1937: China Declares War on Japan[09530]
Chiang Kai-shek
Mao Zedong
Stimson, Henry L.
Hirota Kōki

By 1927, the majority of the warlords in the region had been pacified, and Chiang took advantage of his success to launch a campaign against Mao and his Communist forces. The Kuomintang army inflicted heavy casualties, and the Communists retreated into the safety of the Chinese countryside. By 1928, Chiang felt secure enough to declare that the Kuomintang government was in control of China, and he established his capital in Nanjing. In reality, however, Chiang’s power was tenuous at best, and he had to deal with challenges to his government’s sovereignty from a number of internal and foreign threats. The Kuomintang Party had failed to implement the needed economic reforms, especially in the agricultural sector, that would have helped alleviate the widespread poverty among peasants, and Chiang’s government also faced serious challenges from the warlords, who still pledged their allegiance to the Kuomintang regime but maintained large, independent standing armies and controlled a significant percentage of China’s natural resources.

Chiang also faced a political challenge from Mao and the Communists, who had taken advantage of Chiang’s failed economic reforms to establish strong ties with the peasantry. On an international level, the Chinese Communist Party had called for a military campaign against Japanese incursions into northern China, and Mao also argued for an alliance with the Soviet Union; he believed such an alliance would give China the military strength needed to stop Japan’s aggressive policies.

Japanese expansion into mainland Asia was the most pressing national security threat facing Chiang’s government. Japan’s first target was Manchuria, which occupied territory directly northeast of China. There were three major reasons that the Japanese military sought to control this vital region. Economically, Manchuria possessed great quantities of industrial raw materials, the most important of which were iron ore and coal, which were needed to maintain growth in Japan’s manufacturing and defense sectors. Manchuria also had thousands of square miles of rich, productive farmland, which would help feed Japan’s growing population. Location also played an important role in Japan’s geopolitical worldview, and Manchuria’s strategic position would allow the Japanese to use it as a base of operations against three possible military targets: the Soviet Union, China, and the United States.

In 1894 and 1895, Japan had fought a successful war against China for the control of the Korean Peninsula. The object of this conflict was to drive China from the region because its weak and inefficient military was unable to maintain order in this pivotal strategic area. In addition, the Japanese wanted to block Russian expansion into what Japan believed was its own sphere of influence. Ten years later, in 1904 and 1905, Russia was soundly defeated in the Russo-Japanese War, which established Japan as the premier military power in Asia. If Japan could gain control of Manchuria, it could block any attempts by the new Soviet government to link up with the Chinese Communist army and destabilize the region. Japan could also use Manchuria as a staging area for a future invasion of China. Using the detonation of a small bomb on the Southern Manchurian Railway near the outskirts of Mukden as a sign of Chinese aggression, the Japanese quickly overran Manchuria and established the puppet state of Manchukuo.

In the meantime, relations between Japan and the United States were already tense: The two nations were on a geopolitical collision course over the Nine-Power Treaty, Nine-Power Treaty (1922)[Nine Power Treaty] which assured China’s territorial integrity and served as a bulwark against Japanese domination. As a result of this Japanese aggression, the Western democracies issued a series of condemnations, the most forceful of which came from the U.S. secretary of state, Henry L. Stimson. He convinced the United States to issue the Stimson Doctrine, Stimson Doctrine which refused to recognize Manchukuo’s political legitimacy. Stimson wanted to take more aggressive action, but President Herbert Hoover, like his counterparts in the other capitalist democracies, was too bogged down in the economic chaos of the Great Depression to become involved in an international incident thousands of miles from the borders of the United States. The League of Nations League of Nations openly condemned the aggressive act, and Japan responded by giving up its membership in the international body.

The lack of international response to this blatant aggression unleashed powerful political forces in both China and Japan. In China there was a rapprochement between the Kuomintang government and the Chinese Communist Party; this reconciliation was coordinated by the Soviet Comintern. Communist leaders were concerned about the Japanese drive to control Manchuria, which they believed would isolate the Chinese Communists from their Soviet counterparts. This geopolitical reality convinced Mao to enter into an alliance with Chiang Kai-shek, at least until the threat of Japanese aggression had been overcome.

Japan was also experiencing a period of domestic unrest caused by the struggle between the military and the civilian government. A group of chauvinistic army officers had attacked the civilian government for what they perceived was its weak and incompetent handling of the nation’s diplomacy; they believed the government had disgraced itself in accepting the provisions of the two major treaties of the Washington Disarmament Conference Washington Disarmament Conference of 1922. They viewed the Five-Power Treaty, Five-Power Treaty (1922)[Five Power Treaty] which assigned Japan the smallest ratio of battleships among the world’s major naval powers, and the Nine-Power Treaty, which assured China’s territorial integrity, as betrayals of Japan’s national security. These army officers called for a military takeover of the government, and army death squads assassinated a number of important Japanese officials.

With the approval of the young militarists, a former foreign minister named Hirota Kōki became leader of the new Japanese government. This marked a turning point in the history of Japan and placed the nation’s foreign policy directly in the hands of the military. Once in control, the army began to finalize plans to invade China; their rationale was based on the belief that it was Japan’s responsibility to control events in East and Southeast Asia. This control would be assumed through swift military action followed by the occupation of strategically important areas and, eventually the complete colonization of the region. The Japanese military elite believed that China was decadent, corrupt, and antimodern and that it had abrogated its traditional position of dominance in East Asia.

Japan initiated a series of preliminary military actions to both probe China’s weaknesses and establish staging areas for a massive invasion of the mainland. By the summer of 1937, Chinese and Japanese forces had clashed in battles in both northern and eastern China. The tension between the two nations finally exploded in the Marco Polo Bridge incident just outside Beijing. The nationalist government responded to this incident by declaring war on Japan.


The Japanese army inflicted heavy casualties on the Chinese military and on the segments of the civilian population unfortunate enough to be caught between the two opposing forces. The worst example of Japanese brutality was the Rape of Nanjing. Rape of Nanjing Using a deadly combination of armor, as well as tactical air and ground forces, the Japanese launched a blitzkrieg-like attack against the defenses around Nanjing. The Chinese military was unable to repulse the assault, and the city was quickly overrun. Once inside Nanjing, the Japanese violated and slaughtered thousands of innocent citizens. The military’s failures in Nanjing and other areas caused a significant number of Chinese, especially the peasants, to lose faith in the Kuomintang government. Mao and the Communists would eventually use this lack of confidence to gain power after World War II. Marco Polo Bridge, Battle of the
China;Second Sino-Japanese War[Second Sinojapanese War]
Japan;Second Sino-Japanese War[Second Sinojapanese War]
Second Sino-Japanese War (1937-1945)[Second Sinojapanese War]

Further Reading

  • Graff, David A., and Robin Higham. A Military History of China. Boulder, Colo.: Westview Press, 2002. One of the best surveys of Chinese military history available. Includes maps, bibliography, and index.
  • Hoyt, Edwin P. Japan’s War: The Great Pacific Conflict. New York: Da Capo Press, 1986. Provides a detailed study of Japanese military operations during the period 1931-1945. Includes maps, bibliography, and index.
  • Hsü, Immanuel Chung-yueh. The Rise of Modern China. New York: Oxford University Press, 2000. Among the best single-volume treatments of modern Chinese history. Includes maps, bibliography, and index.

Russo-Japanese War

Chinese Civil War

Japan Withdraws from the League of Nations

Mao’s Long March

Japan Renounces Disarmament Treaties

Rape of Nanjing

Chinese Forces Break Yellow River Levees

Japan Announces the Greater East Asia Coprosperity Sphere

Japan Occupies Indochinese Ports