Like the rest of the world, Japan suffered from the great economic depression of 1929 to 1931. As other countries introduced import tariffs on Japanese exports, the Japanese economic situation rapidly deteriorated. Needing new markets and raw materials, Japan turned its attention to China, knowing that a military conquest of China would give it exclusive control of a large economic area, including markets and raw materials. In 1931, Japan occupied Manchuria and set up the puppet state of Manchukuo to the south. China was militarily weak and could not stem the Japanese advance. By 1933, the Japanese had reached the Great Wall of China.

Japanese expansion into China created friction with the United States and Britain, both of whom had interests in the Far East. The League of Nations condemned the Japanese invasion, and in 1933 Japan withdrew from the League. After this decision, Japan began to...