In Asia, Japan became a rising power and gained more respect from Western powers after its victory in the Russo-Japanese War. Japan joined the Allied Powers in World War I and attacked German colonial possessions in the Far East, adding former German possessions to its own empire. In the 1930s, Japan gained significant influence in Inner Mongolia and Manchuria after it invaded Manchuria. It established Manchukuo, a puppet state in Manchuria and eastern Inner Mongolia. This was essentially the model Japan followed as it invaded other areas in Asia and established the Greater East Asia Co-Prosperity Sphere. Japan went to considerable trouble to argue that Manchukuo was justified by the principle of self-determination, claiming that people of Manchuria wanted to break away from China and asked the Kwantung Army to intervene on their behalf. However, the Lytton commission which had been appointed by the League of Nations to decide if Japan had committed aggression or not, stated the majority of people in Manchuria who were Han Chinese who did not wish to leave China.