It is reasonable to say that WWII began, not with the 1939 Nazi invasion of Poland, but with a battle on the outskirts of Beijing in July 1937.

After occupying Manchuria in 1931, Japan began a wider invasion of China in 1937. By the end of WWII in 1945, ~13-20 million Chinese people had died. Refugees trying to flee the fighting numbered 100 million.

Read this excellent review: History News Network | World War II: From the Chinese Perspective