Clash of the Samurai: the history of Japan’s Genpei War

Hareth Al Bustani introduces us to Japan’s answer to the Wars of the Roses, a samurai civil war that upended centuries of imperial rule and ushered in a military dictatorship – the very first shōgunate

Minamoto fought Minamoto at Uji in 1184, giving the Taira enough time to regroup for a final stand. (Image by Alamy)

Impaled by an arrow, samurai general Minamoto Yorimasa knelt and wrote a farewell poem on his fan: “Like a fossil tree from which we gather no flowers, sad has been my life, no fruit to produce.”

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Accompanied by the symphony of ringing steel and bloodcurdling screams from the battle close by, the 74-year-old calmly pulled out his dagger and cut open his belly, leaving instructions for one of his men to throw his head into the river.

His death, in 1180, is notable as perhaps the first recorded instance of the ritualistic suicide known as seppuku, but unremarkable as one of many caused by the Genpei War, the samurai civil war that swept through Japan at the tail end of the 12th century. Two noble houses, the powerful Minamoto and Taira clans, came to blows over who held the most influence over the emperor on the Chrysanthemum Throne. What followed was five years of bloodshed, falsepromises and backstabbing – a conflict that might better be described as the Japanese Wars of the Roses.

Twelfth-century Japan was technically ruled by an emperor, but the reality was that most of the land – and the military strength – lay in the hands of provincial warlords. Chief among these far-flung powerhouses were the Taira and Minamoto samurai clans. But though they had the might, they lacked the right; prerogative power still lay with the emperor, who held court in modernday Kyoto, then known as Heian. Since its founding as Japan’s capital city, in AD 794, Heian had become a centre of government, headed by an emperor and, by the 10th century, home to around 150,000 people. Temples, shrines, pagodas, landscaped gardens and towers made Heian one of the greatest cities in medieval East Asia.

Who's who in Japan's Genpei War
Who’s who in Japan’s Genpei War (illustration from BBC History Revealed)

In 1156, Japanese emperor Go-Shirakawa found himself in a precarious situation. As was customary, his father (Emperor Toba) had voluntarily ‘retired’ in 1155, ruling from the shadows as a ‘cloistered emperor’. When Toba died, Go-Shirakawa was forced into a brief succession war – against his own brother – in which he was backed by Taira Kiyomori (leader of the Taira samurai clan) and Minamoto Yoshitomo (the son of the Minamoto clan’s leader). In the aftermath, Yoshitomo was ordered to execute his own father for supporting Go-Shirakawa’s brother, but he declined – leaving the deed to a Minamoto officer, who then killed himself in shame.

While Kiyomori rose to unprecedented heights, the sacrifice made by Yoshitomo – now leader of the Minamoto samurai – went largely unrewarded. Just three years later, the bitter Yoshitomo broke out in rebellion, kidnapping Emperor Go-Shirakawa and his son, and leaving a trail of burning buildings in his wake, an event known as the Heiji Rebellion. However, with just 500 men, Yoshitomo was easily defeated by Kiyomori, and later assassinated by one of his own followers. In an act of uncharacteristic mercy, Kiyomori allowed his rival’s three surviving sons, Yoritomo, Yoshitsune and Noriyori, to live in obscurity.

Hero to villain

In the ensuing decades, the capital remained divided between two sources of influence, that of Taira leader Kiyomori and Emperor Go-Shirakawa. When Go-Shirakawa retired to become a cloistered emperor, he appointed a series of puppet emperors that he controlled, bringing in a fresh face every few years.

Meanwhile Kiyomori, the first provincial warrior to be appointed chancellor of the realm, filled the royal court with fellow Taira clan members and the palaces with spies. After uncovering a conspiracy against him in 1177, Kiyomori seized scores of manors and, egregiously and against holy law, tortured and then executed one of the conspirators, a monk named Saiko.

Two years later, Kiyomori placed Go- Shirakawa under house arrest, replaced scores of officers with Taira clansmen and forced the sitting ‘puppet’ emperor to abdicate the throne to his own two-year-old grandson, Antoku.

Furious at being overlooked for the throne, Go-Shirakawa’s son Prince Mochihito found support in the most unlikely of places, the 74-year-old poet Minamoto Yorimasa, who had recently retired from a long military career. Having previously sided with the Taira against his own clan, Yorimasa was described by Kiyomori as a lone beacon of honesty among the Minamoto.

Decades of familial shame finally boiled over when one of Kiyomori’s sons, named Munemori, stole a horse from Yorimasa’s son and mockingly named it after him (the son, that is). Furious, Yorimasa sent word to his Minamoto clansmen and monasteries in the east and north, imploring them to support the rightful emperor Prince Mochihito, and overthrow the Taira once and for all. With just a few hundred followers, the rebels recruited warrior monks from the temple at Miidera, before heading south towards the monasteries of Nara.

When Yorimasa’s warrior monks were intercepted by Taira forces at a small town on the Uji river, they tore up the bridge, mounting an impassioned defence. Taira cavalry were hastily sent across the rapids to deal with them – a gamble that allowed them to overtake and encircle the rebels.

It wasn’t long before the poet Yorimasa carried out his famous seppuku. Prince Mochihito was killed soon after and the great temples of Nara – including the huge 8th-century Todaiji temple complex, once the largest and most powerful temple in Japan – were burned, with 3,500 monks cut down in the process. Though the Taira had acted decisively, Yorimasa’s honourable death had made him a martyr. The Genpei War was about to begin.

(Image by Getty Creative Image/Map from BBC History Revealed)
(Image by Getty Creative Image/Map from BBC History Revealed)

Prodigal sons

Emerging from a life in exile, Yoritomo – the eldest surviving son of the rebellious Yoshitomo, who now claimed leadership of the Minamoto – descended on the mountains of Hakone with a pitiful 200 warriors and was roundly defeated in his first major battle at Ishibashiyama. He escaped and travelled east, scooping up soldiers from sympathetic landowners who had been alienated by the Taira clan’s self-serving tyranny. The following month, having amassed 30,000 men, Yoritomo launched a decisive night attack against a Taira camp.

In March 1181, the Taira were greeted with further ill fortune when their fearless, long-suffering leader Kiyomori died, imploring his sons never to allow Yoritomo’s bones a burial. His son, and successor, the feckless Munemori, faced both dwindling supplies and diminishing support, with many families under the Taira blanket defecting to Yoritomo’s cause. Matters were made worse the following year, when the capital was rocked by famine and pestilence.

When Kiyomori died, he implored his sons never to allow Yoritomo’s bones a burial

Rather than chase the Taira, Yoritomo remained at his base in Kamakura, strengthening his authority in the east (and briefly waging war against his cousin, Minamoto Yoshinaka, until the two joined forces). It wasn’t until 1183, after a series of tug-of-war skirmishes in the north, that the tide finally began to shift in Yoritomo’s favour and he won his greatest victory.

Little is known about the realities of samurai warfare, other than dramatic battle descriptions in war chronicles and epic tales, and the handful of samurai texts that have survived. Trained from childhood, early samurai rode and fought on horseback; upon receiving orders to fight, samurai would leave their fortified manor houses or barracks in a flurry of activity, parading their personal banners and ancient family emblems as they rode off to war. Women played no role in a samurai warrior’s send-off, however; they were not even permitted to be in sight of the warring men in case their ‘yin’ (female) energy affected the ‘yang’ (male) energy that would be required in the battles to come.

Yoritomo's statue stands in Kamakura, the region in which the shogunate he established would rule for 150 years. (Image by Alamy)
Yoritomo’s statue stands in Kamakura, the region in which the shogunate he established would rule for 150 years. (Image by Alamy)

Battle tactics

In June, at Mount Tonamiyama, having gathered his loyal samurai warriors, Yoshinaka fooled 40,000 Taira into thinking his 5,000-strong army was much larger than it really was by erecting a slew of white decoy battle standards atop a hill. The trick worked and the Taira chose to briefly rest on the mountain and water their horses.

Seizing his advantage, Yoshinaka – who had secretly divided his army into three – drew the Taira forces into what seemed like a traditional archery duel, only to sneak the remaining two detachments around them. At sunset, as one unit surprised the Taira rear, another unleashed a stampeding herd of oxen with flaming torches fixed to their horns. In the ensuing chaos, 20,000 Taira warriors were gored. The next month, as Yoshinaka bore down on Heian, cloistered emperor Go-Shirakawa defected to the Minamoto under the guise of a religious pilgrimage. Terrified, Munemori abandoned the capital, taking Antoku with him.

When Yoshinaka arrived soon after (and with his brief war with Yoritomo still in his mind) he began plotting with Yoritomo’s uncle, Minamoto Yukiie, to kidnap Go-Shirakawa and set up a rival government in the north.

However, Yukiie had a change of heart. He revealed all to Go-Shirakawa, who leaked the plot to Yoritomo – he, in turn, commanded his halfbrothers Noriyori and Yoshitsune to attack their ambitious cousin. Enraged, Yoshinaka burned down Go-Shirakawa’s palace, and forced the cloistered emperor to declare him Shogun, which essentially amounted to him becoming a military dictator.

Despite the grandiosity of the title, it was of little consequence – Yoshitsune drove Yoshinaka out of the capital soon after, defeating him at near Uji, and delivering him into the clutches of Noriyori, whose archers shot him down in a rice paddy.

Although the Minamoto infighting allowed the Taira to regroup near modern-day Osaka, they could not have prepared for the genius of Yoshitsune. In early 1184, at the Battle of Ichinotani, he split his army in two, sending the bulk of his forces with Noriyori into some woods, while he led 100 shock cavalry up a mountain overlooking the Taira camp. Come nightfall, as Noriyori attacked, Yoshitsune launched a suicidal charge down the mountain, setting fire to the camp and enveloping the enemy with deadly precision.

The Taira survivors fled to the island of Shikoku, while Yoshitsune returned to the capital a hero. With the jealous Yoritomo yet to recognise his victorious half-brother, Go-Shirakawa took it upon himself to bestow Yoshitsune with honours, sensing an opportunity to divide the Minamoto power base. Meanwhile, Noriyori, who had followed the Taira deep into their traditional heartlands, was struggling to procure supplies, with local lords loathe to hand any over.

Go-Shirakawa sensed an opportunity to divide the Minamoto power base

After a six-month stalemate, Yoritomo finally unleashed Yoshitsune. Riding through the night, Yoshitsune lit fires to give the impression of an enormous invading army, frightening Munemori into abandoning his makeshift palace at Yashima. The Taira leader fled 200 miles west, linking up with Tomomori’s forces along the Shimonoseki Strait. Yoshitsune’s reputation preceded him.

His arrival inspired local magnates to gift hundreds of ships, complete with crews. Finally, in March 1185, he set sail for a climatic showdown at Dannoura to face the combined Taira armies, leaving Noriyori to prevent any escape by land.

Sunken schemes

On 25 April, Kiyomori’s son, Tomomori, who knew the straits better than anyone, sailed out on the early current, choosing to fight where the riptide was strongest. Though he outnumbered the Minamoto, with 450 ships to their 300, by noon the currents had turned on him, and when a prominent admiral defected, Yoshitsune seized the momentum. Facing utter annihilation and preferring to drown rather than be captured, Tomomori leapt into the depths, clad in his heavy armour.

The Minamoto had emerged victorious. The code of honour and ideals (known as Bushido) that guided conduct in war, and for which the samurai are now so famous, would not be fully developed until the 17th and 18th centuries; in the wake of the Genpei War, Taira refugees were hunted down and killed with even the children buried alive, drowned or butchered. Yet more blood was shed within the Minamoto clan itself, as Yoritomo and Yoshitsune struggled for power. But when the formidable Go-Shirakawa died in 1192, and with his rival samurai either murdered or having committed seppuku, Yoritomo made his status official, becoming Japan’s first Shogun.

A visionary if ruthless leader, Yoritomo had delivered the Minamoto to glory, the likes of which no clan had ever known. Though the Minamoto’s supremacy would be squandered by Yoritomo’s sons, the rule of the samurai would last for the better part of a millennium. In the crucible of total war, the samurai identity was crystallised – with a new paradigm of violence for a new order. One where suicide was preferable to capture, and power was laid bare, for whomever was bold enough to seize it.

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Samurai unmasked

While Japan’s central imperial government once held a monopoly over land, by the 10th century, the provinces had been taken over by temples, shrines and private individuals. Landlords not only offered their peasants preferable tax rates, but protection – training them in archery, horse riding and hunting. They developed hierarchies, with long-serving families awarded senior positions, giving rise to the emerging warrior class of samurai.

In the AD 930s, a warrior called Taira Masakado rose up in revolt, declaring himself emperor and seceding the Kanto plain, surrounding modern-day Tokyo. Soon after, the pirate king, Sumitomo – from the powerful Fujiwara clan, who controlled the imperial regency – began raiding the west.

Amidst an outpouring of bloodletting and arson, where soldiers wrenched heads off fallen enemies to prove their prowess, the samurai began to formalise new customs – announcing their names on the battlefield.

Fighting in colourful scale and plate armour, they relished bold shows of individual heroism. The imperial court was only able to suppress the rebels with the aid of provincial warlords. In the next two centuries, the Taira and Minamoto clans would prove valuable allies in suppressing revolts, growing in prestige until they eclipsed even the Fujiwara and, soon enough, the emperor himself.

Hareth Al Bustani is a journalist specialising in the history of Japan.

This article first appeared in the November 2019 issue of BBC History Revealed