Before World War II, Japan built an extensive empire that included Taiwan, Korea, Manchuria, and parts of northern China. The Japanese regarded this sphere of influence as a political and economic necessity, preventing foreign states from strangling Japan by blocking its access to raw materials and crucial sea-lanes, as Japan possessed very few natural and mining resources of its own, although it imported large amounts of coal from Korea, Manchukuo, and some regions of occupied China. Japan's large military force was regarded as essential to the empire's defense.