The League of Nations' response to the Manchurian Crisis of 1931 was a resolution that Japan should withdraw from Manchuria. The Japanese thoroughly ignored the resolution and continued their expansion. In 1933, Japan and China signed a truce, but the area remained in Japanese control.
The Japanese initially invaded Manchuria as a response to the 1931 bombing of a Japanese-owned railway in the city of Mukden. Japan blamed Chinese nationalists for the terrorist attack. Within months, the Japanese had conquered the region and defeated the outmatched Chinese army. Japan renamed the area Manchuko and declared it an autonomous state, although it remained under the control of the Japanese military. It was speculated that Japan used the bombing as a reason to invade and control the resource-rich region since Japan itself was suffering economically from the Great Depression.
The League of Nations was to economically sanction Japan, but instead, it voted to investigate the crisis and ask Japan to withdraw. Finally, a conclusion was reached. After a commission concluded that Japan had violated China's territory, the Japanese delegation walked out on the League and never returned.
During the crisis, the United States, which was not a part of the League of Nations, joined the talks and advised the League to take advantage of the Kellogg-Briand Pact, which was an agreement that made war illegal.