The Second Sino-Japanese War (July 7, 1937 to September 9, 1945), a major war fought between the Republic of China and the Empire of Japan before and during the Second World War, is the largest Asian war in the twentieth century.Although the two countries have fought intermittently since 1931, full-scale war starts in earnest in 1937 and ends only with the surrender of Japan in 1945.

The war is the result of a decades-long Japanese imperialist policy aiming to dominate China politically and militarily to secure its vast raw material reserves and other resources.

At the same time, the rising tide of Chinese nationalism and notions of self determination stoke the coals of war.

Before 1937, China and Japan have fought in small, localized engagements in so-called "incidents".

Yet the two sides, for a variety of reasons, have refrained from fighting a total war.

The 1931 invasion of Manchuria by Japan is known as the "Mukden Incident".

The last of these incidents is the Marco Polo Bridge Incident of 1937, marking the official beginning of full scale war between the two countries.From 1937 to 1941, China fights alone.

After the Japanese attack on Pearl Harbor, the Second Sino-Japanese War merges into the greater conflict of the Second World War.