Excerpts from Books and Wikipedia
"[Japanese army personnel] detonated a small quantity of dynamite close to a railway line owned by Japan's South Manchuria Railway near Mukden (now Shenyang). The explosion was so weak that it failed to destroy the track, and a train passed over it minutes later. The Imperial Japanese Army accused Chinese dissidents of the act and responded with a full invasion that led to the occupation of Manchuria, in which Japan established its puppet state of Manchukuo six months later. The deception was soon exposed by the Lytton Report of 1932, leading Japan to diplomatic isolation and its March 1933 withdrawal from the League of Nations." [Wikipedia] "The Japanese invasion and conquest of Manchuria of 1931–33 was the first big challenge of the post-1919 system. And the system failed. . . . It has often been said that had the Western powers, particularly Britain, France, and the United States, stood firmly against Japan’s invasion of Manchuria, the Second World War would have been averted. As the argument goes, this was the first domino, and if it had been held upright, the others would not have tumbled." [Kennedy: Parliament of Man, Kindle Edition, Location 380-391].