Asia is the world's largest and most populous continent. It covers 8.6% of the Earth's total surface area (or 29.4% of its land area) and it contains more than 60% of the world's current human population.
Much of Asia had been colonized by Europe throughout the 19th century. Japan began asserting itself in the 20th century, taking Spain's possessions. It then aligned itself with Britain and the Entente during the Great War, taking the small territories held by Germany. After the war, Japan took possession of Indochina from France and the Dutch East Indies. It also entered into a conflict with China, which did not quite reach full-scale war.
Britain maintained its own substantial empire in the region, including India. However, in 1943, Japan attacked certain of its former ally's Asian holdings.
Arguably, World War II began in Asia when Japan launched a full-scale invasion of China in 1937. By 1942, Japan had carved a substantial empire out for itself in Asia, when the Raceinvaded. Japan was driven off the mainland of Asia, although it was able to maintain toe-holds in the surrounding islands.