Overview

Between the 12th and mid-19th centuries Japanese warfare remained largely unchanged. A military force was made up of Samurai and land-owning soldiers under the authority of a Shogun or Warlord. This state of technological stability would remain largely in place for over 700 years, until the end of the Sakoku period of Japanese isolation, after which trade with the West brought with it new arms and equipment. In a drastically short period of around 30 years, the Japanese went from a medieval level of warfare where swords and armor ruled to a technological level rivaling or surpassing that of the Civil War era United States.

Medieval Period

o-yoroi, circa 12c                         do maru, circa 16c

The Japanese medieval period, also known as the Feudal Period, was one largely marked by clan warfare under the daimyos (feudal lords) as with the successful repulsion of the Mongol invasions of the 1200's,  warfare in Japan saw a turn from ritualized tournament-style battles to large open-field conflicts, often with thousands or tens of thousands to a side. It was in this period that the art of weapon and armor-smithing became popularized, aided by the development of "Japanese Steel", a metallurgy technique extremely advanced for the time which allowed the creation of powerful blades (such as the famous katana) and nearly impenetrable armor. It was during this time that the tradition of the Samurai shifted from their original role as archers to that of swordsmen and cavalry.

During this period, while Japan was still technically a monarchy, in reality the central government held little power, with the actual authority held by the various warlords and daimyos. Because of this warfare became a constant aspect of Japanese life for hundreds of years at a time. It was during the late medieval periods that gunpowder weaponry was first introduced in the form of arquebuses acquired from Dutch traders. While highly inaccurate and extremely limited in supply, the arquebuses could prove devastating when well-utilized, and could be operated by conscripted ashigaru foot soldiers as they required little to no training to operate.

An early Japanese Arquebus, circa late 16c

The late medieval military remained in a period of relative stagnation during the Edo Period of 1603 - 1867 CE. This period saw a large drop in military conflicts after the Siege of Osaka in 1614 and also saw the implementation of Japanese isolationism known as Sakoku, under which no Japanese national could leave the archipelago nor could any foreigner enter under pain of death, and trade was officially limited to the Chinese and Dutch. After nearly 200 years, pressures from the west mounted as the US and European nations sought trading strongholds outside of China. Finally, on July 15th, 1843 US Naval forces under the command of Commodore Matthew C. Perry sailed into Uraga Harbor and forcibly ended Sakoku under threat of attack.

Transition to the Modern Period

Depiction of the Japanese military, circa 1900

With the arrival of international trade inevitably came weapons manufacturers wishing to sell their wares. In 1873 the Japanese Imperial Government instituted a program of national conscription and established the Imperial Japanese Army. The feudal system was all but wiped out, with resisting clans and daimyos swiftly being crushed by superior numbers and equipment (an artistic rendition of which can be seen in The Last Samurai, starring Tom Cruise). Almost overnight the Japanese military had transformed from hundreds of waring domains into a mostly unified modern military power.

The next decades would see Imperial Japan claim victory after victory, first in the First Sino-Japanese War, then in Japanese Invasion of Taiwan and afterwards the Ruso-Japanese War. It was this last conflict that truly marked Japan as a full military power, and was the first time an asian military had defeated a European power since Genghis Kahn. Japan would go on to play a relatively minor role in World War I on the side of the Allies, and would use its military might to claim much of the Pacific in the lead-up to World War II. 

Japan's defeat in World War II would effectively end the concept of a modern Japanese military. After the war, its armed forces were disbanded, and the Emperor was forced to sign a constitution outlawing the use of force as a political tool (except in self-defense) as part of the surrender agreement. Now, the Japanese armed forces exist as a shadow of their grand past in the form of the Japanese Self-Defense Forces, which fulfill a similar roll to that the National Guard serves in the US.

See Also:

Japanese Self-Defense Forces