While Japan has always had a strong individual warrior tradition (e.g., bushido), Japanese militarism primarily refers to the increasingly important role of the organized military in government, beginning with the Meiji Restoration of 1838. Radical military officers had a considerable role in starting World War Two in the Pacific, particularly in the 1920-1940 period. Eventually, militarism reduced the decision space of grand strategy to the assumption that only military needs would meet Japan's goals.
Karel von Wolferen, who has long explained Japanese political behavior, even after the war, in the lack of central authority led the increased role of the military, who were under little or no civilian control of the military, and who were split into independent Army and Navy structures.  argues that the Japanese decision for war in 1941 came directly from rivalry and lack of information exchange between the Imperial Japanese Army and Navy. The Army, having been fighting in East Asia for a number of years, was the more militant of the two services, while Isoroku Yamamoto was transferred from vice-Navy Minister to Commander-in-Chief, Combined Fleet, to better protect him against radical assassins angry at his advice against war.
The Army, on setting Japan on the path to war took it for granted that the Navy would take care of defense against U.S. might, while the Navy, wishing to hold onto its power and its credibility as a patriotic institution, refrained from directly expressing the belief, widespread among its ranks, that victory was impossible. 
While the usual meaning of the term deals with matters prior to 1945, Edwin Hoyt and others argue that there may be a post-1945 trend toward militarism. They argue that Article 9 of the postwar Constitution, banning war as an instrument of national policy, has not been fully effective. 
While there is much historical work on what these officers did, there has been much less analysis on why the Japanese system of government could be so affected by them. One reviewer summarizes theories that include:
- "A breakdown of the decision-making processes in the civilian and military sectors;
- an internal response to external traditions
- poor leadership
- the inherent Japanese military tradition
- a reaction against urbanization
- the plot or plan thesis versus the drift-into-war thesis.
Another set of reasons, which considers Western imperialism as the key driver, is:
- Japan's desire to be a Western-style imperialist power
- Japan's concerns for its security
- Japan's belief in its leadership role for Asia
- Japan's frequent provocations by Western powers
- Japan's desire to secure its economic interest
The shishi movement, which began with emphasis on supporting the Emperor, was based of kokutai, or the Japanese national polity for which the Emperor was father figure, and sometimes a deity. As such, the shishi have been considered predecessors of the militarism of the 20th century.
Ruth Benedict in her first war-oriented study of Japanese motivation, saw a fundamental difference in the Western and Japanese view of society. Western thought recognizes individuals, and, at a higher level, a multipolar system of sovereign nations. She connected this the two parts of the shishi motto, "Revere the emperor and expel the barbarians," and that wartime Japan, with certain exceptions, expelled Western political principles. Germany and Italy, in the Tripartite Pact, certainly were not endorsing multipolarity.
An essential part of Japanese culture, however, that every person has a "proper station" in a hierarchy, and this principle extends to a hierarchy of nations. She quoted a Japanese military spokesman in 1942, extending the traditional view of the role of the elder brother. Speaking of the Greater East Asian Coprosperity Sphere, he said
Japan is their elder brother and they are the younger brothers. This fact must be brought home to the inhabitants of the occupied territories. Too much consideration shown for the inhabitants might engender in their minds the tendency to presume upon Japan's kindness with pernicious effect on Japanese rule.
Gekokoju became, in the 1920s and 1930s, an institutionalized system of insubordination by junior and mid-level officers. Its theory held that obedience to superiors was less important than obedience to principles, above all, that of kokutai . It can also be translated as "insubordination", but as a means of redressing social injustice, which arose in the fifteenth century when provincial lords disobeyed the shogun and the shogun disobeyed the emperor. 
It could justify assassinations and overthrows of government. Gekokoju was practiced both by middle and senior officers against the government, as in the Manchurian Incident, and by junior officers, as in the February 26, 1936 Incident.
A striking example of attempted civilian control of the military occurred with the 1930 London Naval Conference, in which Prime Minister Osachi Hamaguchi named Reijiro Wakatsuki, another civilian, as chief delegate plenipotentiary to it, an unprecedented role for a civilian.
- Karel van Wolferen (1989), The Enigma of Japanese Power: People and Power in a Stateless Nation, Alfred E. Knopf, pp. 39-40
- Sadao Asada, "The Japanese Navy and the United States" in Dorothy Berg & Okamoto Shumpei (eds.), Pearl Harbor as History, Columbia University Press, 1973, pp. 258-259, quoted in von Wolferen, pp. 39-40
- Edwin T. Hoyt (1985), The Militarists: the Rise of Japanese Militarism since WWII, Donald I. Fine, ISBN 0917657179 Cite error: Invalid
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- Sandra T. Jamison, "The Rise of Militarism in Prewar Japan: A Critical Review", Chung Chi Journal
- Bill Gordon (March 2000), Japan's March Toward Militarism, Wesleyan University
- Mikiso Hane (1990), Premodern Japan: a historical survey, Westview Press, ISBN 978-0813380650, pp. 214-217
- Ruth Benedict (1946), The Chrysanthemum and the Sword: Patterns of Japanese Culture, Signet reprint from Houghton Mifflin, p. 53
- Tetsuo Najita & H.D. Harootunian, Japan's Revolt against the West, in Bob Tadashi Wakabayashi, Modern Japanese thought, Cambridge University Press, pp. 208-209
- John Toland (1970), Chapter 1: Gekokoju, The Rising Sun: the Decline and Fall of the Japanese Empire 1936-1935, vol. Volume 1, Random House, p. 5