In the First World War, Japan joined the Allied powers, but played only a minor role in fighting German colonial forces in East Asia. At the following Paris Peace Conference of 1919, Japan's proposal of amending a "racial equality clause" to the covenant of the League of Nations was rejected by the United States, Britain and Australia. Arrogance and racial discrimination towards the Japanese had plagued Japanese-Western relations since the forced opening of the country in the 1800s, and were again a major factor for the deterioration of relations in the decades preceding World War 2. In 1924, for example, the US Congress passed the Exclusion Act that prohibited further immigration from Japan.
After WW1, Japan's economical situation worsened. The Great Kanto Earthquake of 1923 and the world wide depression of 1929 intensified the crisis.
During the 1930s, the military established almost complete control over the government. Many political enemies were assassinated, and communists persecuted. Indoctrination and censorship in education and media were further intensified. Navy and army officers soon occupied most of the important offices, including the one of the prime minister.
Already earlier, Japan followed the example of Western nations and forced China into unequal economical and political treaties. Furthermore, Japan's influence over Manchuria had been steadily growing since the end of the Russo-Japanese war of 1904-05. When the Chinese Nationalists began to seriously challenge Japan's position in Manchuria in 1931, the Kwantung Army (Japanese armed forces in Manchuria) occupied Manchuria. In the following year, "Manchukuo" was declared an independent state, controlled by the Kwantung Army through a puppet government. In the same year, the Japanese air force bombarded Shanghai in order to