The Ishiyama Hongan-ji War (石山合戦, Ishiyama Kassen) was a ten-year military campaign that took place from 1570 to 1580 in Sengoku period Japan, carried out by lord Oda Nobunaga against a network of fortifications, temples, and communities belonging to the Ikkō-ikki, a powerful faction of Jōdo Shinshū Buddhist monks and peasants opposed to the rule of the samurai class.

Quick Facts Siege of Ishiyama Hongan-ji, Date ...

Siege of Ishiyama Hongan-ji
Part of the Sengoku period
The battle of Ishiyama Hongan-ji by Utagawa Yoshifuji (1828-1887)
Date August 1570 – August 1580 Location Osaka, Fortress of Ishiyama Hongan-ji; other ikki strongholds Result Oda victory, Kōsa surrenders
Belligerents
forces of Oda Nobunaga	Ikkō-ikki monks forces of Ashikaga Yoshiaki[1] Mōri clan
Commanders and leaders
Oda Nobunaga Sakuma Nobumori Niwa Nagahide Akechi Mitsuhide Harada Naomasa † Araki Murashige Takayama Ukon Hosokawa Fujitaka Inaba Yoshimichi Andō Morinari Ikoma Chikamasa	Kōsa Shimozuma Nakayuki Shimozuma Rairyū Saika Magoichi Ashikaga Yoshiaki Rokkaku Yoshikata Mori Terumoto
Strength
at least 30,000	at least 15,000

Close

It centered on attempts to take down the Ikki's central base, the cathedral fortress of Ishiyama Hongan-ji, in what is today the city of Osaka. While Nobunaga and his allies led attacks on Ikki communities and fortifications in the nearby provinces, weakening the Hongan-ji's support structure, elements of his army remained camped outside the Hongan-ji, blocking supplies to the fortress and serving as scouts.

The Ikkō-ikki leagues of warrior monks and commoners were among the last to stand in the way of Oda Nobunaga's bid to conquer all of Japan. Oda and Tokugawa had fought the Ikki before, crushing their armies of Mikawa Province and other areas, and by 1570, their twin fortresses of Ishiyama Hongan-ji and Nagashima were their last bastions of strength. He besieged both fortresses simultaneously, attacking Ishiyama in August 1570 and Nagashima in 1571.

In August 1570, Oda Nobunaga left Gifu Castle in Gifu with 30,000 troops, and ordered his generals to build fortresses around Ishiyama, while Nobunaga himself focused on the Sieges of Nagashima fortress and other campaigns. On September 12, the Ikkō-ikki launched a midnight stealth attack against Nobunaga's forces at Kawaguchi and Takadono. The Ikko were reinforced by warrior monks from Negoro-ji in Kii Province and 3,000 musketeers, pushing Oda's army back.^[2][3][4] Nobunaga's armies remained camped out, assigned to monitor the Ikki's fortress, and take it if they could.

In 1574, after destroying the Nagashima complex and reducing the threat from the Ikki's supporters, Oda attempted to starve out the fortress. This was no easy task, however, because the Ishiyama fortress sat on the coast, which was guarded by the fleet of the Mōri clan, masters of naval combat and Oda's enemies.

By early 1575, however, the fortress was already in urgent need of supplies, and the Abbot Kōsa was ready to begin peaceful overtures with Nobunaga to end the siege. But the ousted shōgun Ashikaga Yoshiaki sent a letter to Mōri Terumoto asking for his aid in supplying the cathedral fortress.^{[4]: 288–289} Yoshiaki eventually raised some troops himself to aid the besieged.^[1]

With respect to Imperial order, Nobunaga spared the lives of many of the defenders, including Shimozuma Nakayuki, but burned the fortress to the ground.

In the same year, following the fall of the Honganji, Nobunaga accused Sakuma Nobumori and dismissed Ando Morinari from Nobunaga's service.

Three years later in 1583, Toyotomi Hideyoshi would begin construction on the same site, building Osaka Castle, a replica of which was constructed in the 20th century.