In This Article Expand or collapse the "in this article" section Medieval Japan, 900-1600

  • Introduction
  • Economics

Military History Medieval Japan, 900-1600
Michael F. Solecki
  • LAST REVIEWED: 28 November 2016
  • LAST MODIFIED: 28 November 2016
  • DOI: 10.1093/obo/9780199791279-0165


Famine, drought, disease, pestilence, and dirty politics forced total civil war on the Japanese people from 900 CE to 1600 CE. The imperial court established military reforms placing higher responsibilities on the provincial governments, eventually weakening the court. Mercenary groups of samurai were bought and sold as private armies; with the right deal, even changing sides mid-battle was common. The situation forced peasants into supporting these armies with goods and services above their own needs. The imperial court (based on the Confucian model) and the emperor (believed to be divine) after a short time became a figurehead. Maintaining law and order, day-to-day governing, and collecting taxes were delegated to mid-level samurai aristocrats with their private mercenary armies at the provincial level. Ethics were not always practiced among the samurai. Daimyo verbally laid down ethics codes, and a few even had them written down. As military needs grew, the legitimate laws called the Taiho Code also began to decay. Stimulated by natural disasters, by 1185 daimyo were in a constant battle for productive farmlands. Fleeting samurai honor lead to treachery, espionage, subterfuge, etc. In 1192, the northern Kanto provinces far from the capitol began to rebel. The imperial court/regent was forced to establish a local military-led shadow government (bakufu) to keep the peace. Leadership was a samurai general (shogun) and a retired emperor for a perceived legitimacy. In 1274 the Mongol Kubilai Khan unsuccessfully attempted an invasion; in 1281 he tried again, unsuccessfully after a relatively short war of attrition. The economic and loyalty problems continued. By 1477, family alliances across Japan were in constant flux. In 1543 the Portuguese arrived, complicating matters by bringing Christianity and trade with the West. They also introduced finely made handheld firearms and cannons. These firearms changed the face of Japanese warfare and eventually allowed a resourceful samurai to unify Japan into a nation. The constant warfare brought religion (a syncretism of Buddhism and Shinto) to the forefront, becoming a means of emotional survival for both commoners and aristocrats alike. Some saw the new Christianity as a means of solace, while others saw it as a way to get better trade deals with the Portuguese Jesuits. In 1571, Oda Nobunaga joined with the Toyotomi and Tokugawa samurai families, intending to unify Japan through the triumvirate. A long thirty-year war ensued. Nobunaga was killed in 1583, allowing Toyotomi Hideyoshi to finally unify Japan in 1590. Hideyoshi, seeing the Japanese as a superior race, decided to unify and rule East Asia as well, and in 1592, he invaded Korea with plans to use it as a platform to overtake China. The war, popularly known as the Imjin War, ended in 1598 with Japan retreating home, followed by the death of Hideyoshi. His heir-apparent was too young to rule. The triumvirate agreement had Tokugawa Ieyasu ruling until Hideyoshi’s heir was of age and mopping up the last traditional strongholds, ending with the Battle of Sekigahara in 1600. Soon after, Tokugawa had Hideyoshi’s heir assassinated, took over and became shogun, and brought a new order of civility to Japan and nearly three hundred years of peace.

General Overviews

The history of Japan during the period from 900 to 1600 CE “is” a military history. The “total war” atmosphere that spanned this eight-hundred-year period forced the entire population into participating. In order for a researcher to grasp the Japanese propensity for war, it is important to understand the origins of the Japanese people and the mental and physical environment they experienced. The complexity of the Japanese culture can make it difficult to focus on one historical topic without over stepping into others. Readers not familiar with Japan prior to 900 CE should reference the appropriate Oxford Bibliographies article Military History of Japan (origin to 900 AD), or for a quick, light/easy reference, read Morton and Olenik 2005; it is brief, well organized by timeline, and briefly covers the periods of origin leading up to the early 21st century in accurate but simple terms. It provides the general public with a place to start a more comprehensive project. The publications listed in this section are a mix of comprehensive chronologic and lighter-side overviews of Japan suited for both serious researchers and casual curiosity. Throughout this section and the article as a whole, the historiography varies. Much of the information comes from ancient Chinese texts translated into Japanese and then into English, or directly into English as well. Both the casual reader and the serious researcher can have difficulty understanding the texts. It is recommended that the reader, especially the serious researcher, try and do comparative reading to get two or more sources rather than settle on one source. The historiographies of the selections included in this section are considered the main stream, as they are the basic overview of the period. The selections included throughout the rest of the article are more detailed, focusing on a specific topic and as intended, lean more toward the individuals’ perceptions of the interpretation of one or more primary and/or secondary source. The reader, therefore, should not be surprised if there are what appear to be slight contradictions in facts among particular interpretations.

  • Morton, W. Scott, and J. Kenneth Olenik. Japan: Its History and Culture. 4th ed. New York: McGraw-Hill, 2005.

    Good for a quick, easy-to-read reference for chronology and background; not a lot of detail and written at a general education level.

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