The Second Sino-Japanese War (July 7, 1937 ??September 2, 1945), called so after the First Sino-Japanese War of 1894??5, was a military conflict fought primarily between the Republic of China and the Empire of Japan from 1937 to 1941.

China fought Japan with some economic help from Germany (until 1941), the Soviet Union (1937??940) and the United States. After the Japanese attack on Pearl Harbor in 1941, the war merged into the greater conflict of World War II as a major front of what is broadly known as the Pacific War. The Second Sino-Japanese War was the largest Asian war in the 20th century. It also made up more than 50% of the casualties in the Pacific War if the 1937??941 period is taken into account.