The Zenkunen and Gosannen Wars (1051-1087) and Japanese Swords: The Warrior Culture Cultivated by the Minamoto Clan in Eastern Japan

The Zenkunen and Kogo Wars—The Age of the Warrior Class Born in Tohoku

In the late Heian period, two major internal conflicts erupted in Mutsu Province (present-day Tohoku) as their stage. These were the Zenkunen War (1051–1062) and the Kogo War (1083–1087). These conflicts were not mere provincial rebellions, but rather pivotal historical turning points that determined the rise of the Minamoto warrior clan, who would later establish the Kamakura shogunate, and they had a profound impact on the development of the Japanese sword.

The Zenkunen War began when the imperial court dispatched Minamoto no Yoriyoshi as Mutsu no Kami (Governor of Mutsu) in response to the expanding power of the Abe clan, a dominant local clan in Mutsu. With the support of the Kiyohara clan, Yoriyoshi destroyed the Abe clan, and through his military achievements, the Minamoto established a firm foothold in the eastern provinces. In the subsequent Kogo War, Minamoto no Yoshiie (also known as Hachiman Taro Yoshiie) intervened in internal conflicts within the Kiyohara clan and suppressed them, solidifying the Minamoto's status as the "chief of the warrior class" in the eastern provinces.

The Battlefields of Tohoku and the Practical Utility of Swords

The terrain of the Tohoku region, where the Zenkunen and Kogo Wars were waged, provides important context for the development of swords during the Heian period. In close-quarters combat in mountainous and forested areas, while mounted archery was the primary response method, the practical utility of swords played a decisive role in grappling from horseback and close-range combat.

The Japanese swords used during this era corresponded to the early stage of the "old sword period" (kokataki). Slender tachi with pronounced waist curvature (koshizori) were the mainstream, and their design assumed single-handed operation from horseback. The blade length typically ranged from two shaku seven sun to three shaku (approximately 82–91 centimeters), and the characteristic features of tachi from the middle to late Heian period were deep curvature and a relatively small kissaki.

In one of the fierce battles of the Zenkunen War, the Battle of Kinomi in 1057, Minamoto no Yoriyoshi and his son Yoshiie suffered a major defeat against the forces of Abe no Sadatō. Records of this defeat indicate that many soldiers were killed in close-quarters combat after arrows ran out, illustrating the intensity of sword-based melee combat. Conversely, in the decisive battle of the Battle of Kuriayagawa in 1062, Yoshiie's forces, with reinforcements from the Kiyohara clan, achieved an overwhelming victory, and Abe no Sadatō was killed.

Minamoto no Yoshiie and the Establishment of "The Way of Bow and Arrow"

The exploits of Minamoto no Yoshiie during the Kogo War (1083–1087) were passed down to posterity as the origin of Japanese bushidō. Particularly famous is the anecdote of "geese in disarray." The story goes that while advancing, Yoshiie observed a flock of geese flying overhead suddenly break formation, which allowed him to detect the presence of an ambush and avoid disaster. This anecdote is widely known as symbolic of a military commander's insight.

Yoshiie was known during this campaign not only as an excellent archer but also as a skilled swordsman. The samurai who served under him were based in the eastern provinces and sought to maintain cutting-edge practical forging techniques for swords. Mutsu Province was also known as a source of iron sand, and it has been suggested that Tohoku's iron-working culture may have been utilized in sword production.

Tohoku's Iron-Working Culture and the Sword Industry

The Tohoku region in the Heian period was not merely a battlefield, but also an important region in iron-working technology. The Ōshū region (Mutsu and Dewa) had abundant sources of iron sand, and local iron workers (tetshi) conducted iron sand refinement. This Tohoku iron culture is thought to have supported weapons supply for the Minamoto warrior clan.

Specifically, multiple traces of sword production have been confirmed in the vicinity of Hiraizumi, the center of the Ōshū Fujiwara clan (a successor force to the region that served as the stage for the Zenkunen and Kogo Wars in a later period). Archaeological surveys have uncovered blacksmith remains dating from the late Heian period to the early Kamakura period across the Tohoku region, gradually revealing the reality of local sword production.

On the other hand, most of the samurai who participated in the Zenkunen and Kogo Wars were from the Kanto (Bandō) region, and their swords are thought to have been primarily commissioned from master smiths in Kyoto, Yamato, and Bizen. While local blacksmiths handled weapon replenishment and repairs at distant campaign sites, the production of renowned swords remained in the hands of central sword-making groups.

The Minamoto Warrior Clan's Sword Culture and Its Legacy

The sword culture of the Minamoto warrior clan, established through the Zenkunen and Kogo Wars, directly influenced the later warrior government's perspective on swords. In the Minamoto lineage spanning from Yoshiie to Yoritomo, swords were positioned not merely as weapons, but as symbolic embodiments of samurai authority and legitimacy.

Particularly noteworthy is the relationship between Minamoto no Yoriyoshi and Yoshiie and the Ise Grand Shrine. The Minamoto chose Hachiman as their clan deity and established the custom of presenting swords to the Tsurugaoka Hachiman Shrine (Kamakura). This tradition of sword presentation originated from prayers for victory and offerings of gratitude during the Zenkunen and Kogo Wars, and later became the precedent for sword presentations by warrior clans to shrines.

The "tale of Yoshiie's virtue," wherein Yoshiie, unrewarded for his military achievements in the Kogo War, used his own funds to bestow rewards upon his retainers, became widely known in the medieval period and beyond. As this anecdote demonstrates, the samurai culture of symbolizing master-retainer relationships through swords—the acts of presenting, gifting, and offering swords—became established as a Minamoto tradition through the conflicts of Tohoku.

The Significance of the Zenkunen and Kogo Wars in Sword History

The Zenkunen and Kogo Wars hold several important meanings in the history of the Japanese sword. First, by establishing the rise of the Minamoto warrior clan and opening the path to the later establishment of a warrior government (the Kamakura shogunate), these wars laid the foundation for the development of the entire samurai culture centered on the Japanese sword.

Second, the large-scale battles in the provincial region of Tohoku increased demand for practical swords and catalyzed the refinement of tachi styles capable of accommodating both mounted combat and close-quarters combat.

Third, the custom established during this era of "the chief of the warrior class bestowing swords upon his retainers" elevated the Japanese sword beyond a mere weapon to a social symbol. This legacy was inherited from the late Heian period through the Kamakura and Muromachi periods and into the Edo period, forming the cultural foundation upon which the Japanese sword came to be called "the soul of the samurai."