The Manchurian Incident, commonly known as the Mukden Incident, was an explosion staged by rogue military officials in the attempt to justify the Japanese invasion of northeastern China, or Manchuria, in 1931. Fueled by economic and political interests, the incident involved placing a small amount of dynamite next to a Japanese-owned railway line near Mukden on Sept. 18, 1931.
While the explosion was minor, it was enough to anger the Japanese Imperial Army, who accused the Chinese of staging the explosion, leading to the invasion of the northeastern region of China.
Due largely to an unprepared Chinese military, the Japanese seized control of the entire region within months, strengthening its control on the resource-rich territory.
While the United States did engage in trade and investment with China, there was little support for punishing the Japanese because of the 1930s depression, and the U.S. did not take military action. It did, however, try to convince the League of Nations, though unsuccessfully, to enforce the 1928 Kellogg-Briand Pact signed by the two countries, which prohibited the war.
As a result, the United States issued the "Stimson Doctrine" in early 1932, stating it would not recognize any agreements between China and Japan that limited free trade in the region.