Short answers, pulled from the story.
Japanese militarism was the ideology that military strength was equal to national strength and that the military should dominate Japan's political and social life. It was most prominent from the introduction of universal conscription in 1873 until Japan's defeat in World War II in 1945.
Major Jakob Meckel was a Prussian military advisor sent to Japan from 1885 to 1888 at Japan's own request. He reorganized Japan's army into divisions and regiments, connected military bases by railway, trained roughly sixty of Japan's highest-ranking officers, and introduced Clausewitz's theories along with the Prussian concept of war games.
Japanese law required the posts of Army Minister and Navy Minister to be filled by active-duty officers nominated by their respective services. Because a prime minister could not form a cabinet without these posts filled, both the Army and Navy held an effective veto over any civilian government and could bring it down by withdrawing their minister.
The Manchurian Incident of September 1931 was a staged provocation in which Kwantung Army conspirators blew up a section of South Manchurian Railway track near Mukden, blamed Chinese saboteurs, and used the event as a pretext to invade and seize all of Manchuria. The civilian government in Tokyo was powerless to stop it.
Notable opponents included Prime Minister Hara Takashi, who was assassinated in 1921; diplomat Kijuro Shidehara, whose non-interventionist policy was attacked by military interests; Baron Takuma Dan, director of Mitsui Bank, murdered on the 5th of March 1932; and Tokugawa Iesato, who met with President Roosevelt in 1933-1934 to encourage resistance to rising militarism.
Japanese militarism was discredited by Japan's military defeat and the American occupation that followed. Former military leaders were tried for war crimes before the Tokyo tribunal, and pacifism was written into Japan's postwar constitution as a central tenet. The occupation lasted until the 28th of April 1952.