They condemned Japan who simply quit the League in response; they took no direct military intervention
The Japanese military largely dismissed the League of Nations' condemnation of its invasion of Manchuria in 1931. They viewed the League as ineffective and continued their military expansion, asserting that their actions were justified for Japan's security and economic interests. In response to the League's criticisms, Japan ultimately withdrew from the organization in 1933, further solidifying its stance and pursuing aggressive policies in the region.
In 1931 Japan invaded Manchuria. To cover up their invasion, the Japanese imposed a new "puppet" government (a government controlled by them) that was meant to approve their presence in Manchuria. The name of Manchuria changed to Manchukuo and therefore so did the name of the government. The League of Nations sent a commission to investigate whether or not the Manchurians really wanted the Japanese there called the Lytton Commission. They determined that, in fact, the Japanese were not welcome in Manchuria. This basically eventually lead to the Japanese withdrawing from the League of Nations.
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The Japanese conquest of Manchuria and the Italian conquest of Ethiopia both showed the weaknesses that were in the League of Nations agreement.
The first example is the Japanese invasion of Manchuria. The League of Nations disapproved but had no means to stop the invasion. Mussolini then invaded Ethiopia in 1935, and the League of Nations was unable to take action against him. Finally, in 1936, Hitler began to remilitarize Germany, and there was no reaction from the League of Nations.
Japan, Germany and Italy
The Japanese invasion of Manchuria in 1931The invasion of Abbysinia by Italy in 1935The re-militarisation of the Rhineland by Germany in 1936All these were aggressive actions, but whether they threatened world peace is debatable.
They demonstrated the ineffectually of the League of Nations, which certainly must have emboldened Hitler to attempt territorial acquisitions of his own.
Japan attacked Manchuria in 1931 and subsequently setup a puppet state, Manchuko. Manchuria is the Chinese area bordering on Russia and its invasion caused China to seek a remedy from the League of Nations. The League censored Japan, and the Japanese delegation walked out of the meeting, leaving Japan isolated from the rest of the world.
Japan decided to invade Manchuria the day after the Mukden incident, in 1931. However, the entire state of Manchuria was not conquered until 1932, so the answer to the question is 1932.
First of all, action against a country required a unanimous vote in the League of Nations. As a member of the League of Nations, Japan also had to the right to veto the action. Several members had valuable trade agreements, and were reluctant to vote to apply sanctions on Japan since it might hurt their agreements. As a result, the League of Nations was a failure, and Japan remained in Manchuria.
The occupation of the Rhineland, the invasion of Manchuria, and the invasion of Ethiopia are examples of aggressive expansionism and militarism by authoritarian regimes in the 1930s. These actions were driven by a desire for territorial expansion and were significant precursors to World War II. They highlighted the failure of the League of Nations to maintain peace and the growing tensions that ultimately led to global conflict.