Iwai Rebellion vs Hayato Rebellion

The Yamato army followed a standard punitive expedition doctrine. Iwai initially established a static defense and naval blockade but failed to develop an alternative strategy in the face of Yamato's determined advance.

The Yamato army adapted from an initially successful rapid assault to a prolonged siege when faced with unexpected resistance, demonstrating doctrinal flexibility. The Hayato opted for fortified defense over guerrilla tactics and failed to adapt to changing conditions. Yamato converted the pincer maneuver into an attrition strategy at Soonoiwaki and Himenoki, achieving final success.

Battle of Annihilation

Siege/Challenge

Mononobe no Arakabi successfully applied the Center of Gravity principle by directing the main body of his troops at the Tsukushi region, where Iwai's headquarters were located. Iwai, on the other hand, failed to achieve strategic focus by dispersing his forces to different provinces.

The Yamato command identified the Hayato's seven castles as the center of gravity and struck them directly. Although Ōtomo no Tabito's decision to return temporarily weakened the Schwerpunkt, the vice-generals sustained the operation. The Hayato side was forced to split its center of gravity among scattered castles.

Silla's bribery and instigation of Iwai against Yamato can be assessed as an indirect military deception. Yamato, instead of a direct military ruse, triumphed through overwhelming force and rapid movement.

Yamato masked its military preparations by keeping the Hayato engaged through the earlier deployment of 5,000 settlers and administrative pressure. The bekkokushi expeditions gathered intelligence under the guise of exploration. There is no record of deception or intelligence tricks on the Hayato side; they followed a direct uprising strategy.

As weapon technology of the period was limited to swords, spears, and bows, a classic shock effect was limited. However, the cavalry units of the Mononobe clan were used as a tactical shock element against Iwai's infantry lines, causing them to scatter.

The Yamato army conducted systematic assaults on the castles with archers and close-combat units, but it was the relentless siege tactics in the final phase that created a psychological shock among the Hayato. The Hayato side, though outnumbered, inflicted surprise losses on Yamato through sorties from their fortified positions. Overall, firepower and shock effect were limited; victory was achieved through attrition.

The mountainous and forested terrain of Tsukushi was suitable for Iwai's guerrilla-style resistance. However, the final pitched battle took place in an open field where Yamato's disciplined infantry could leverage its advantage.

The volcanic 'shirasu' soil of southern Kyushu, unsuitable for rice cultivation, was the fundamental factor that triggered the rejection of the Ritsuryō system. The Hayato turned this barren terrain to their advantage by building fortified castles. Yamato leveraged seasonal logistical advantages (spring-summer campaign) to gain operational superiority against the castles. The climate tested Yamato's endurance during the prolonged sieges.

Thanks to intelligence from Silla, Iwai was aware of Yamato's military preparations and its route. However, Yamato did not entirely overlook the rebellion preparations; the appointment of Mononobe indicates the court had some knowledge of Iwai's intentions.

Yamato gathered information on the political fragmentation and geographical defense points of the Hayato through bekkokushi (exploratory delegations). The Hayato, on the other hand, could not foresee Yamato's central court decisions and rapid mobilization capacity; thinking they had provoked a sudden reaction by killing the local governor, they were caught unprepared for the speed of Yamato's countermove. The intelligence asymmetry played a critical role in Yamato's operational timing.

The Yamato army could not achieve strategic surprise moving by sea to Kyushu; however, after landing, it sought a decisive outcome by directly targeting Iwai's forces in a rapid interior line maneuver. Iwai attempted to fight on multiple fronts by dispersing his troops, but this dispersion became a weakness against the central force.

Yamato forces, executing a planned pincer movement, captured five castles within three months, effectively applying the principle of interior lines. Even after Ōtomo no Tabito returned to the capital, the operational tempo was maintained, demonstrating maneuver flexibility. The Hayato, by remaining in a static defense, lost their interior-line advantage.

Sanctified by imperial edict, the Yamato soldiers possessed a high sense of legitimacy against the forces of Iwai, who were branded as 'rebels'. Local elements on Iwai's side, on the other hand, suffered a moral collapse due to accusations of being 'foreign collaborators' stemming from the Silla alliance.

The Hayato warriors were highly motivated to defend their independence and communal land system; the resistance shown in the last two castles is evidence of this. On the Yamato side, institutional obedience under imperial authority and the fear of punishment provided moral superiority. In the context of Clausewitz's 'friction,' the Hayato's hunger and attrition during the prolonged siege gradually eroded their morale.

Silla succeeded in instigating Iwai to distract Yamato from Korea and create an internal conflict. This diplomacy-based maneuver is an early example of the principle of defeating the enemy without direct combat by wearing him down.

The Yamato court had been encircling the Hayato culturally and demographically since 702 through administrative restructuring (establishment of Satsuma and Ōsumi provinces) and by settling 5,000 people from Buzen. However, this peaceful assimilation attempt backfired because it threatened the Hayato land system, escalating tensions after the 700 threat incident. Ultimately, the strategy of winning without fighting failed, necessitating direct military intervention.