The Second Sino-Japanese War (July 7, 1937 ??September 9, 1945) was a military conflict fought primarily between the Republic of China and the Empire of Japan. After the Japanese attack on Pearl Harbor, the war merged into the greater conflict of World War II as a major front of what is broadly known as the Pacific War.

Although the two countries had fought intermittently since 1931, total war started in earnest in 1937 and ended only with the surrender of Japan in 1945. The war was the result of a decades-long Japanese imperialist policy aiming to dominate China politically and militarily and to secure its vast raw material reserves and other economic resources, particularly food and labour. Before 1937, China and Japan fought in small, localized engagements.

Yet the two sides, for a variety of reasons, refrained from fighting a total war. In 1931, the Japanese invasion of Manchuria by Japan's Kwantung Army followed the Mukden Incident. The last of these incidents was the Marco Polo Bridge Incident of 1937, marking the beginning of total war between the two countries.