Tenshō Iga Disturbance

Iga Province, corresponding to the mountainous regions of what is now northwestern Mie Prefecture, had developed its own autonomous system called 'sōkoku' since ancient times. It possessed a unique social structure where the distinctions between samurai, farmers, and ninja were ambiguous, and demonstrated a strong spirit of independence against external powers. In particular, it was known as the birthplace of 'Iga-ryū ninjutsu,' where ninja clans, including the Hattori family, refined their skills in intelligence gathering and ambush tactics based on their deep knowledge of mountains and wilderness.

First Invasion Failure (Tenshō 7)

In Tenshō 7 (1579), Oda Nobukatsu (Nobunaga's second son) launched an invasion of Iga on his own authority. However, this was a reckless military action conducted with insufficient preparation, and he suffered a major defeat against the organized resistance of Iga's regional lords and ninja. Nobukatsu's forces were confounded by Iga's surprise attacks and guerrilla tactics, executed by those with superior knowledge of the mountain terrain, losing many soldiers and forced to retreat.

Nobunaga severely rebuked this failure and ordered Nobukatsu to remain in confinement. However, for Nobunaga, who aimed to unify the realm, Iga's independent forces could not be overlooked.

Preparation for Second Invasion

In the summer of Tenshō 9 (1581), Nobunaga decided on a full-scale invasion of Iga. While Nobukatsu was nominally the supreme commander, Nobunaga actually directed all military operations. The mobilized forces numbered between 40,000 and 60,000 troops according to various accounts. A strategy of siege and annihilation was employed, with simultaneous invasions from multiple directions to encircle Iga.

Powerful generals under Nobunaga's command—Takigawa Kazutoki (Ise direction), Gamo Ujisato (Ōmi direction), and Niwa Nagahide (Yamato and Yamashiro directions)—each took charge of their respective sectors, deploying their forces to encircle Iga from all four sides. Regarding weaponry, a plan was made for the massive deployment of firearms, with the strategy of overwhelming Iga's mountain guerrilla tactics through sheer numbers.

Course of Battle—Annihilation in Days

In early September of that year, the Oda forces, beginning their invasion from all directions, captured Iga's major strongholds one after another within days. Iga's regional lords and the defensive forces of the sōkoku coalition mounted tenacious resistance in various locations, but they could not maintain organized resistance in the face of overwhelming numerical superiority and the power of firearms.

Those holed up in mountain castles and fortifications were put to death, and many who attempted to flee were cut down. It is said that Nobunaga showed no mercy toward Iga's resistors in particular, taking no prisoners and ordering complete annihilation—hence the reason it was later called the 'Great Massacre of Iga.'

However, many ninja abandoned organized combat and survived by hiding deep in the mountains. Some Iga ninja, including lineages of Hattori Yasushiro (father of Hattori Hanzō), had begun serving Tokugawa Ieyasu early on (in the context of the 'divine lord's passage through Iga'), and had already placed themselves under Tokugawa protection just before the Tenshō 9 disturbance.

Ninja Weapons and Their Relationship to the Japanese Sword

The Iga Disturbance is noted as a historical example where the weapon culture of ninjutsu directly confronted the sword culture of samurai. Ninja weapons, designed primarily for assassination, reconnaissance, and deception rather than direct confrontation, centered on small, portable implements such as kunai, shuriken, grappling hooks, and smoke screens.

However, when full-scale combat ensued, ninja also used swords. The use of swords in Iga-ryū ninjutsu differed from standard swordsmanship, characterized by practical multipurpose applications such as defensive and striking techniques using the scabbard and using the sword as a foothold when climbing walls. Furthermore, the swords carried by ninja (ninja-tō or shinobi-tō) were shorter than standard swords and had a shape closer to a straight blade, prioritizing maneuverability in confined spaces.

On the other hand, swords produced in Iga during this period were recognized as 'Iga blades' with their own distinctive reputation, and practical swords made by mountain smiths were known for prioritizing durability over decoration. The fact that the Iga Disturbance decimated many of these local blade smiths became a point of rupture in the history of Iga swords.

Nobunaga's Realm Unification Policy and the Significance of Iga

The conquest of Iga was an important part of Nobunaga's vision for realm unification. Nobunaga's political philosophy of destroying the remnants of medieval decentralized order (autonomous sōkoku) and extending centralized control nationwide was manifested in his systematic attacks on regions with independent self-governing systems, such as Iga, Negoroji, and Saiga (Kii Province).

After subjugating Iga, Nobunaga granted Iga Province to Nobukatsu and had him implement a disarmament policy that became the prototype for land surveys and the later sword hunts. This policy—confiscating swords, spears, and bows from peasants and concentrating all military force exclusively in the samurai class—became the precursor to the 'Sword Hunt Edict' (Tenshō 16, 1588) that Toyotomi Hideyoshi would later implement after his own realm unification.

The year after the Iga Disturbance, in June of Tenshō 10 (1582), the Honnō-ji Incident occurred and Nobunaga died in an unexpected reversal. However, Iga's organized self-governance never revived, and the ninja clans scattered to serve as mercenaries and intelligence agents for various daimyo. It is transmitted that some of their techniques and weapons covertly influenced the formation of swordsmanship schools during the Edo period.

The Ninja Sword and Its Place in Sword History

The Tenshō Iga Disturbance occupies a special place in the history of the Japanese sword. In normal campaigns, swords forged by renowned smiths were borne at the waist of commanders, their sharpness and curve supporting their martial achievements. However, the swords used by Iga ninja were unmarked, practical tools—swords as implements.

The collision between these two sword cultures—the Japanese sword as an aesthetic and spiritual culture of samurai and the ninja sword as a practical and secretive culture—represents one of the rarest historical moments in sword history. The fact that modern ninja trends and sword games frequently use Iga and Kōga as themes may be said to reflect an unconscious resonance with this historical background.

The Tenshō Iga Disturbance, in which Nobunaga's firearms units clashed with Iga's ninjutsu, is an event that should be remembered in both sword history and military history as one of the conflicts that heralded the end of the Sengoku period—namely, the end of the era in which swords were the principal instruments of warfare on the battlefield.