Manchuria crisis, happened in 1931, was about China invaded by Japan. Japanese sent the army to China in order to get out of the depression. They took Manchuria, which was in the northeast of China, and renamed it as Manchukou. The League of Nations sent Lytton Commission, trying to make sure what was happening between Japan and China. However this took almost a year to finish investigating. After the League of Nations received Lytton Report, the League finally started to condemn Japan, asking it to give Manchuria back to China. But Japan refused this and left the League in 1933.
This apparently showed the how weak the League of Nations was. The League tried to take sanction against Japan. But it was useless. Japan's major trading partner was the U.S., which was not belonged to the League. In addition, Some European countries, such as Britain, didn't want to charge sanction to Japan because they wanted to sell their goods. Economic sanction was the harshest punishment that the League of Nations had. Furthermore, Britain and France didn't want to fight a war against Japan. Eventually the League of Nations lost its honor because they even couldn't stop a small Asian country invading the other.
Another famous crisis that humiliated the League of Nations was Abyssinian crisis. In 1935 Italy let by Mussolini sent 400,000 troops to Abyssinia, trying to take it over. Italy harshly used modern weapons, such as poison gas to invade Abyssinia with poor army. Apparently, the League of Nations should stop Italy, but what