Events leading to Japanese aggression By edamameflower Sep 18, 1922 Hungary joins League of Nations Hungary joins the League of Nations, which creates even more of a threat to Japan. Jun 4, 1928 Japan assassinates Zhang Zuolin Japan assassinates the Manchurian warlord Zhang Zuolin, which causes even greater tension. Apr 22, 1930 Regulation of submarine warfare Italy, Japan, the UK, & the USA sign the London Naval Treaty which regulates the utilization of submarine warfare. Sep 19, 1931 Japan invades Manchurian The Japanese invasion of Manchurian triggers the fighting of the second Sino Japanese War May 20, 1936 The signing of the Anti-Comintern Pact Japan & Germany sign the Anti-Comintern Pact that's directing against communism in the Soviet Union. Jul 7, 1937 Marco Polo Bridge Incident The Marco Polo Bridge Incident was a battle between China & Japan, start of the second Sino War.