<P> The Mukden Incident, also known as the "Manchurian Incident" was a decisive setback that weakened The League because its major members refused to tackle Japanese aggression . Japan itself withdrew . </P> <P> Under the agreed terms of the Twenty - One Demands with China, the Japanese government had the right to station its troops in the area around the South Manchurian Railway, a major trade route between the two countries, in the Chinese region of Manchuria . In September 1931, a section of the railway was lightly damaged by the Japanese Kwantung Army as a pretext for an invasion of Manchuria . The Japanese army claimed that Chinese soldiers had sabotaged the railway and in apparent retaliation (acting contrary to orders from Tokyo,) occupied all of Manchuria . They renamed the area Manchukuo, and on 9 March 1932 set up a puppet government, with Pu Yi, the former emperor of China, as its executive head . This new entity was recognised only by the governments of Italy, Spain and Nazi Germany; the rest of the world still considered Manchuria legally part of China . </P> <P> The League of Nations sent observers . The Lytton Report appeared a year later (October 1932). It declared Japan to be the aggressor and demanded Manchuria be returned to China . The report passed 42--1 in the Assembly in 1933 (only Japan voting against), but instead of removing its troops from China, Japan withdrew from the League . In the end, as British historian Charles Mowat argues, collective security was dead: </P> <Dl> <Dd> The League and the ideas of collective security and the rule of law were defeated; partly because of indifference and of sympathy with the aggressor, but partly because the League powers were unprepared, preoccupied with other matters, and too slow to perceive the scale of Japanese ambitions . </Dd> </Dl>

When did japan leave the league of nations