In what year did world war 2 began?

Officially, World War II began in Asia when the USA was brought in to the war in December of 1941. However, Japan had been expanding their sphere of influence in Asia long before then. Japan began major imperial expansion in the Russo-Japanese War of 1904, and they continued this trend until they were defeated in World War II. If you lived in China during World War II, you didn't call the war "World War II:" you knew it as the Sino-Japanese War, which began officially in 1937 and lasted until Japan's defeat in 1945.