Swords in Late Kamakura and the Kenmu Restoration: Post-Mongol Samurai Society

The Impact of the Mongol Invasions—Battle with Foreign Enemies Changed the Sword

The Mongol Invasions (represented by the Bunei Campaign of 1274 and the Koan Campaign of 1281) dealt a grave military and political blow to Japan's warrior society. The coalition forces of Mongolia, Goryeo, and the Southern Song employed the following tactics and weapons.

• Massed formations
• Poisoned arrows
• Tetsuhauo (exploding projectiles)

These were fundamentally incompatible with Japanese samurai culture, which idealized one-on-one honorable mounted combat, and many gokenin found themselves in dire straits before massed infantry and fire-based suppression tactics.

The greatest impact the Mongol invasions had on the Japanese sword was "the enlargement of the blade." To counter the Mongol military's thick iron armor (lamella-type), demand arose for longer, thicker, and heavier blades. Whereas the traditional tachi had a blade length of around 70–75 cm, from the late Kamakura period through the Nanbokucho era, "odachi" (great swords) and "nodachi" (field swords) with blade lengths exceeding 90 cm appeared—this was a direct response to these practical battlefield demands. The increase in foot combat also reinforced this trend; longer swords that could be wielded powerfully with both hands became more advantageous on the battlefield than single-handed weapons worn at the hip.

Furthermore, after the Mongol invasions, discontent among the gokenin regarding postwar settlement deepened. Since the Mongol invasions were defensive campaigns, the shogunate could not distribute land seized from enemies as rewards. Inadequate compensation reached those gokenin who risked their lives in battle, and a rift developed particularly between eastern gokenin dependent on shogunate authority and powerful western samurai clans. At this time, the sword remained a symbol of merit and reward, and inequity in its distribution directly touched upon the honor and lives of warriors themselves, becoming a distant cause of the shogunate's eventual collapse.

The Rise of Sword-Makers in the Late Kamakura Period—An Age of Competing Schools

From around the time of the Mongol invasions through the end of the Kamakura period, Japanese sword production centers in Yamato, Soshu, and Mino rapidly gained strength alongside Yamashiro and Bizen, establishing the framework of the five schools (Gokasen).

In Yamato, the following five major schools were perfected, establishing the distinctive Yamato tradition style of straight blades and finely straight temper lines:

• Tegai school
• Senjuin school
• Taima school
• Shikkake school
• Hossho school

Through deep relationships with major temples such as Kasuga Taisha, Todai-ji, and Kofuku-ji, Yamato sword-makers produced a wide range of works from practical blades for temple warriors to decorative swords for nobles, enjoying a unique production environment supported by religious authority. Their forging grain was characterized by masame as the foundation, with hamon featuring tightly closed nioiguchi—embodying restrained beauty.

In Soshu (Kamakura), "Shintogo Kunimitsu" emerged, opening the path to the later flourishing of the Soshu tradition—Masamune and Sadatsugu. Kunimitsu's blades were characterized by strong nie and vigorous jihada, earning high praise as a sword-maker who achieved both practical battlefield demands and aesthetic value at the highest level. The fact that Soshu was the center of the Kamakura shogunate brought sword-makers and samurai power closer together, creating fertile ground for the highest-quality commissioned blades. The tachi by Kunimitsu housed in the Tokyo National Museum conveys through its dignified and powerful construction the origins of the later Soshu tradition to the present day.

Emperor Godaigo and the Kenmu Restoration—Blades as Proof of Political Legitimacy

Through the Genko Incident of 1331 and the Shokei Rebellion of 1333, Emperor Godaigo overthrew the Kamakura shogunate and inaugurated the "Kenmu Restoration." However, this regime collapsed in just three years, and Ashikaga Takauji seized Kyoto and established the Northern Court (Muromachi Shogunate). Emperor Godaigo fled to Yoshino and established the Southern Court, opening more than sixty years of Nanbokucho civil war.

In this turbulent age, the sword functioned beyond mere weapon—as "proof of legitimacy." Generals of both the Godaigo and Ashikaga factions began bestowing renowned blades as rewards for military service, and sword ownership became a means of visualizing political loyalty. "Which master sword-smith's blade do you wear?" and "From whom did you receive your blade?" became symbols denoting a general's position and status, and the social meaning of the sword grew ever more layered.

Particularly notable during the Kenmu regime period were the blade collections said to be held by generals such as Kusunoki Masashige and Nitta Yoshisada, who served Emperor Godaigo closely, and many Yamashiro and Yamato sword-makers engaged in their work with backing from either the Southern or Northern Court. This structure, in which political patronage and the sword-maker's economic survival became inseparable, vividly illustrates a pattern repeated throughout Japanese blade history: that master craftsmen could pursue the pinnacle of technique by adhering closely to specific holders of power.

Technical Changes from Late Kamakura Through Kenmu Period—Establishment of Bold, Powerful Construction

Technically, distinct changes in blade form appeared from the late Kamakura period through the Kenmu era. The "fukura" (the swelling of the kissaki section) became more pronounced, and the curve's center of gravity shifted from "koshi-zori" toward "naka-zori" (center curvature). This was a rational shape change designed to endure the impact of downward strikes on the battlefield while maximizing cutting power.

In the hamon, variants of gunome and choji developed, and nie-deki hamon came to be admired. Nie refers to the fine, gleaming particles appearing at the boundary of the temper line—visible evidence of the metal's microstructural change produced by variations in fire temperature. In particular, Soshu tradition masters like Kunimitsu and his successors made abundant use of ara-nie, greatly expanding sword aesthetics from calm, balanced beauty to bold, wild beauty.

The process by which the "perfected beauty"—restrained construction and symmetrical elegance—completed in mid-Kamakura transformed into "magnificent beauty" through an age of warfare represents the essence of blade technology in this era. While responding to battlefield demands, sword-makers did not sacrifice aesthetic perfection; instead, they discovered new beauty within strength.

Bridge to the Nanbokucho Turmoil—The Age Tempered the Sword

Amid the tumultuous historical upheaval of the Mongol invasions' shock, the Kamakura shogunate's collapse, the Kenmu Restoration, and the Nanbokucho division, the Japanese sword continued its technological evolution while meeting practical battlefield demands. The tendency toward "enlargement and magnificence" established in this period directly led to the subsequent era of Nanbokucho dominance of the odachi and nodachi.

During the Nanbokucho period of warfare, odachi with blade lengths exceeding one meter were produced in vast quantities, and scenes of mounted warriors sweeping enemy positions from horseback became as routine as foot soldiers carrying swords on their backs during marches. The productive capacity supporting such demand lay precisely in the communities of sword-makers in the five schools that flourished across regions from the late Kamakura period through the Kenmu period.

The phenomenon of "mass production of blades," which became pronounced during the Nanbokucho period, also had its roots in that age's political confusion and chronic warfare. Not only artistic blades by master craftsmen but mass-produced practical swords came to be demanded on a large scale, dramatically expanding the economic scale and social role of sword-smiths.

This age, in which historical upheaval fundamentally transformed the appearance of the Japanese sword, is positioned in blade history as a "period of transformation." From the tachi of mid-Kamakura, when aesthetic sensibilities of peaceful times reached their apex, to the odachi of the Nanbokucho period, grown magnificent in response to warfare's demands—the blades of the late Kamakura and Kenmu periods that formed this bridge are an indispensable chapter for understanding the diversity and fundamental strength of the Japanese sword.