Wars of Japan’s Unification (1560–1615)

The wars of Japan’s unification were a long series of battles, sieges and political deals in which a few powerful warlords brought the whole of Japan under one government. They began in 1560, when Oda Nobunaga, a lord of part of Owari province (around modern Nagoya), destroyed an invading army at Okehazama, and they ended in 1615, when the Tokugawa captured Osaka Castle and the last heir of Toyotomi Hideyoshi died.

Japanese historians call the goal of these wars tenka tōitsu, “unifying the realm under heaven”. The word tenka at first meant the capital region around Kyoto, where the emperor and the shogun lived, and only gradually came to mean the whole country. The years from Nobunaga’s entry into Kyoto in 1568 to Sekigahara in 1600 are also called the Azuchi–Momoyama period, after the castles of Nobunaga and Hideyoshi.

The wars were not one war with two sides. Alliances changed all the time. Tokugawa Ieyasu fought for the Imagawa in 1560, alongside Nobunaga from 1562, against Hideyoshi in 1584 and for him afterwards, and against Hideyoshi’s son in 1614. Religious communities, especially the Ikkō-ikki leagues of the Jōdo Shinshū sect, were among the strongest armed powers of the age.

Oda Nobunaga (1534–1582) was the son of a middle-ranking lord. He was bold, quick to use new weapons and often ruthless. From 1567 he used a seal reading Tenka fubu, usually translated “the realm under military rule”. By the time of his death he controlled about a third of Japan, including the capital.

Toyotomi Hideyoshi (1537–1598) was born into a humble family in Owari and rose in Nobunaga’s service from low rank to become one of his leading generals, under the name Hashiba. After Nobunaga’s death he defeated his rivals, took the court titles of kampaku (imperial regent) and daijō daijin, and by 1590 was obeyed by every lord in Japan. He then launched two invasions of Korea (1592–1598), known in Korea as the Imjin War, which failed.

Tokugawa Ieyasu (1543–1616) spent part of his childhood as a hostage and was allied with Nobunaga for twenty years. Hideyoshi moved him to the Kantō region in 1590, and he built up Edo (modern Tokyo) as his base. After Hideyoshi’s death he won at Sekigahara, became shogun in 1603 and destroyed the Toyotomi in 1615. His descendants ruled Japan until 1868.

In 1560 Imagawa Yoshimoto marched west through Owari with a large army. Nobunaga, with a much smaller force, attacked his camp at Okehazama and killed him. The Imagawa never recovered, and their young vassal Matsudaira Motoyasu — later Tokugawa Ieyasu — made his own alliance with Nobunaga. In 1567 Nobunaga took Inabayama Castle in Mino and renamed it Gifu.

In 1568 Nobunaga escorted Ashikaga Yoshiaki, the brother of a murdered shogun, to Kyoto, and Yoshiaki became the fifteenth shogun. The two soon quarrelled. Yoshiaki encouraged a ring of enemies against Nobunaga: the Asai and Asakura, the Enryaku-ji monasteries on Mount Hiei, the Ikkō-ikki of Hongan-ji, and Takeda Shingen, who crushed Ieyasu at Mikatagahara in 1573. Nobunaga fought back, burned Mount Hiei in 1571, and in 1573 drove Yoshiaki out of Kyoto and destroyed the Asakura and Asai. Shingen died on campaign the same year.

In 1575 Oda and Tokugawa troops using massed arquebuses behind wooden palisades defeated Takeda Katsuyori at Nagashino. Nobunaga built a grand new castle at Azuchi on Lake Biwa, besieged the fortified temple of Ishiyama Hongan-ji in Osaka for ten years until it surrendered in 1580, and sent Hideyoshi west against the Mōri. In the spring of 1582 his armies destroyed the Takeda.

On the 2nd day of the 6th month of 1582 (21 June in the Western calendar of the time), Nobunaga was staying at the Honnō-ji temple in Kyoto with few guards. His general Akechi Mitsuhide surrounded the temple with his army, and Nobunaga died in the fire. His eldest son and heir died the same day.

Hideyoshi was besieging the Mōri castle of Bitchū Takamatsu when he heard the news. He quickly made peace, marched his army about 200 kilometres back towards Kyoto in about a week, and defeated Mitsuhide at Yamazaki eleven days after Honnō-ji. In 1583 he beat Nobunaga’s senior general Shibata Katsuie at Shizugatake and began building Osaka Castle.

In 1584 Hideyoshi fought Ieyasu and Nobunaga’s son Nobukatsu at Komaki and Nagakute. Ieyasu won the main battle, but Hideyoshi won the war by making a separate peace with Nobukatsu, and Ieyasu later became his vassal. Hideyoshi conquered Shikoku in 1585 and Kyushu in 1587, when the powerful Shimazu of Satsuma submitted. In 1590 he besieged the Hōjō in Odawara, and the lords of the north came to swear loyalty. For the first time in over a century, every region of Japan obeyed one ruler.

When Hideyoshi died in 1598 his son Hideyori was five years old. Ieyasu, the strongest of the regents, and Ishida Mitsunari, one of Hideyoshi’s administrators, became bitter rivals. In 1600 their armies — the Eastern Army and the Western Army — met at Sekigahara. Several Western lords changed sides during the battle, and Ieyasu won in a single day.

Ieyasu became shogun in 1603, but Hideyori still lived in Osaka Castle with great wealth and prestige. In the winter of 1614 Ieyasu besieged Osaka; the defenders held out, and a truce was agreed. In the summer of 1615 the Tokugawa attacked again, won the battles of Dōmyōji and Tennōji, and captured the burning castle. Hideyori and his mother killed themselves, and the age of civil wars was over.

The Ashikaga shoguns had ruled Japan from Kyoto since the fourteenth century, but their authority depended on great provincial governors (shugo). The Ōnin War of 1467–1477, fought in and around Kyoto between factions of these governors, left the capital in ruins and the shogunate powerless. Historians usually date the start of the Sengoku period to this war.

Over the following century real power passed to regional lords, the Sengoku daimyo. Many of them — the Hōjō in the Kantō, the Mōri in the west, even the Oda — were new men who had overthrown or replaced their former superiors, a trend contemporaries called gekokujō, “the low overthrowing the high”. The strongest built territorial states with their own law codes, land surveys, castle towns and armies of vassals and conscripted farmers.

Other powers were not daimyo at all. Leagues of villagers and local samurai (ikki) governed whole provinces such as Kaga and Iga. The Jōdo Shinshū (True Pure Land) temple network centred on Ishiyama Hongan-ji in Osaka could call on tens of thousands of armed believers. Great monasteries such as Enryaku-ji owned estates and kept armed forces. Cities such as Sakai were run by merchant councils.

Why did Nobunaga, rather than a greater lord, begin the unification? Historians point to the rich rice lands and trade routes of Owari and Mino, which lay close to Kyoto, to his use of the shogun and the emperor to legitimise his actions, and to luck: the deaths of Takeda Shingen in 1573 and Uesugi Kenshin in 1578 removed his most dangerous enemies at critical moments.

Portuguese traders brought matchlock guns to Tanegashima island in 1543, and Japanese smiths were soon making them in large numbers at places such as Sakai and Kunitomo. By the 1570s arquebuses (teppō) were standard equipment for foot soldiers (ashigaru), used together with long pikes and bows. Nagashino in 1575 became the symbol of this change, though historians now think the story of a perfectly timed, three-rank rotating volley is a later embellishment.

Armies grew enormously. Battles of the early Sengoku period often involved a few thousand men; Hideyoshi is said to have mobilised well over 200,000 for the Odawara campaign of 1590, and both sides at Sekigahara fielded tens of thousands each. Such armies needed roads, supply depots, fleets and careful logistics, and Hideyoshi in particular was a master of siege by starvation and flooding, as at Miki, Tottori and Bitchū Takamatsu.

Castles changed too. Earlier fortresses were mostly earthworks on hilltops. Nobunaga’s Azuchi Castle (begun 1576) combined high stone walls with a multi-storey keep (tenshu) richly decorated inside, and it served as a residence, a political stage and a symbol of power. Hideyoshi’s Osaka and Fushimi castles and the Tokugawa castles that followed spread this style across Japan. Castle towns grew around them and became the ancestors of many modern Japanese cities.

Nobunaga’s longest war was not against a daimyo but against Hongan-ji. From 1570 to 1580 its head, Kennyo, called on believers to resist, and Ikkō-ikki forces fought Nobunaga in Osaka, Nagashima, Echizen and Kaga. Nobunaga answered with extreme violence. At Nagashima in 1574 he ordered the killing of the besieged communities as they came out to surrender. In 1580 Hongan-ji finally accepted a settlement mediated by the emperor and left Osaka.

In 1571 Nobunaga’s troops burned the temples of Enryaku-ji on Mount Hiei, the most important centre of Tendai Buddhism, which had sheltered his enemies. Contemporary diaries describe thousands of victims. Modern excavations have found fewer traces of burning than these accounts suggest, so the scale is debated, but the attack shocked contemporaries and shaped Nobunaga’s later image as a destroyer of Buddhism.

Christianity arrived with Francis Xavier in 1549. Nobunaga allowed Jesuit missionaries to preach in Kyoto and Azuchi, partly to balance the Buddhist institutions and partly out of interest in European goods, and some daimyo converted. In 1587, at the end of the Kyushu campaign, Hideyoshi issued an edict ordering missionaries to leave, although it was not strictly enforced at first; the Tokugawa later banned Christianity completely. The unification thus ended the military power of religious institutions and placed all religions under the control of the state.

Hideyoshi turned military victory into a lasting system. His nationwide land surveys (Taikō kenchi) measured fields and assessed them in koku of rice, so that every lord’s domain had a known value. His sword hunt of 1588 ordered farmers to hand over their weapons, and later decrees fixed the line between warriors, who lived in castle towns, and farmers, who stayed in the villages. Lords could be moved from one domain to another at his order.

The Tokugawa kept and refined these policies. The shogunate controlled the major cities and mines, arranged the daimyo into trusted house vassals (fudai) and former rivals (tozama), and later required them to spend alternate years in Edo. The Laws for the Military Houses of 1615, issued just after the fall of Osaka, limited castle building and alliances between lords.

The result was an unusually long peace. From 1615 to the 1860s there was no major war inside Japan apart from the Shimabara rebellion of 1637–38. Samurai became administrators, cities and trade grew, and the culture of the Edo period flourished. The same unified military power had also made possible Hideyoshi’s invasions of Korea in 1592–1598, whose results are described in the article on the Imjin War.

Chronicles of the unification tend to celebrate great generals, but the wars fell hardest on ordinary people. Armies lived off the land, burned villages to deny supplies to the enemy, and seized people as well as goods. Contemporary sources describe captives being sold, sometimes to foreign traders, a practice that the 1587 edicts discuss.

Sieges by starvation, which made Hideyoshi’s reputation, meant slow death for the defenders and for the townspeople and farmers who had fled into the castles. Accounts of Tottori in 1581 describe terrible famine inside the walls. Religious communities suffered massacres at Mount Hiei, Nagashima and in Echizen, and the invasion of Iga in 1581 is remembered locally as a catastrophe.

Numbers of dead in the sources are usually round figures written to impress, and modern historians treat them with caution. What is clear is that the peace which followed was built on the destruction of many independent communities — villages, leagues, temples and towns — that had governed themselves during the Sengoku period.

During the Edo period the Tokugawa shogunate encouraged histories that presented Ieyasu as a patient, wise founder, and he was worshipped as a deity (Tōshō Daigongen) at Nikkō. Hideyoshi, whose line the Tokugawa had destroyed, was officially played down, but popular books such as the Taikōki made his rise from peasant to ruler a favourite story.

After the Meiji Restoration of 1868, the three unifiers were reinterpreted as national heroes. Hideyoshi, in particular, was celebrated in the age of Japanese imperialism for his invasions of Korea — the same wars that Koreans remember as a national catastrophe and a story of resistance. Nobunaga became the model of the modernising innovator, an image still popular in novels, television dramas, films and video games.

Views outside Japan differ. For Korea and China the key figure of the period is Hideyoshi the invader, not Hideyoshi the unifier. Within Japan, too, historians have moved away from the “great man” story towards the study of villages, religious communities, trade and the experience of ordinary people, and many older legends about the three unifiers have been questioned.

The most important narrative source for Nobunaga is the Shinchō kōki (Chronicle of Lord Nobunaga) by his former retainer Ōta Gyūichi, compiled after 1582 from notes he kept at the time. Historians regard it as generally reliable in dates and places, though it presents Nobunaga favourably; an English translation by J. S. A. Elisonas and J. P. Lamers appeared in 2011. For Hideyoshi, Oze Hoan’s Taikōki (1620s) is livelier but less reliable.

Contemporary diaries of courtiers and priests, such as the Tokitsugu kyōki, the Kanemi kyōki and the Tamon’in nikki of Kōfuku-ji, record events day by day from the point of view of Kyoto and Nara. Thousands of letters and orders issued by the warlords themselves survive and form the documentary backbone of modern research. Jesuit letters and Luís Fróis’s História de Japam give outsiders’ descriptions of Nobunaga, Hideyoshi and their cities.

Much of the popular image of the wars, however, comes from later works: the Kōyō gunkan, a Takeda military text compiled in the early seventeenth century; Tokugawa-era histories such as the Mikawa monogatari and the official Tokugawa jikki; and military histories written by the Imperial Japanese Army General Staff in the late nineteenth and early twentieth centuries. Their dramatic details — troop numbers, speeches, clever stratagems — are often unconfirmed by earlier sources.

Dates are a further problem for readers outside Japan. Japanese sources use era names and the lunisolar calendar, so the 2nd day of the 6th month of Tenshō 10 (Honnō-ji) corresponds to 21 June 1582 in the Julian calendar then used in Europe. English-language works usually give Julian dates before October 1582 and Gregorian dates afterwards; conversion tables such as the one published by the National Astronomical Observatory of Japan are the standard tool, and small discrepancies between books are common.

Revolutionary or conventional? The older view of Nobunaga as a radical innovator who deliberately set out to destroy the medieval order has been challenged. Jeroen Lamers’s Japonius Tyrannus (2000) and much recent Japanese scholarship emphasise how much Nobunaga worked within existing institutions, cooperating with the court and for years with the shogun, and how many of his “innovations” had precedents among other daimyo.

Battles and legends. At Okehazama the traditional story of a surprise attack circling round behind the Imagawa camp comes mainly from later works, and some historians argue for a more direct assault. At Nagashino, the famous three-rank volley fire by 3,000 arquebusiers is not described in the earliest sources, and historians doubt both the numbers and the tactic, stressing instead the field fortifications and the Takeda decision to attack them. At Sekigahara, the story that Ieyasu forced Kobayakawa Hideaki to defect by firing on his position was questioned by Fujimoto Masayuki as early as 1984, and the famous Oyama council before the campaign has also been doubted because of conflicts with contemporary letters.

Why Honnō-ji? Akechi Mitsuhide’s motive has produced many theories: personal grievance, ambition, fear for his own position, loyalty to the court or the shogun, or conspiracy by others. Letters found in the Ishigai family papers, published in 2014, drew attention to the “Shikoku theory”: Nobunaga’s decision to attack Chōsokabe Motochika, with whom Mitsuhide’s circle had close ties. No theory is accepted by all historians.

Periodisation and the idea of unification. Historians disagree about whether the process should be dated from 1560, 1568 or 1573, and whether it ended in 1590, 1600 or 1615. Some question the teleological term “unification” itself, since the participants did not know how things would end and many fought to preserve local autonomy. Comparative historians place Japan’s unification alongside other early modern state-building processes, such as the consolidation of Joseon, Ming and Qing China, the Mughal empire and the European monarchies.