The Sieges of Karasawayama Castle occurred on nine or more occasions from the Eiroku era (1558 to 1570) to the Genki era (1570 to 1573) in Shimotsuke Province.  The conflict was waged between Uesugi Kenshin (a daimyō and the sixteenth head of the Yamanouchi-Uesugi clan of Echigo Province) and Sano Masatsuna (a sengoku daimyō and the fifteenth head of the Sano clan of Shimotsuke Province).

Karasawayama Castle was in a strategic location in the southern portion of Shimotsuke and Uesugi Kenshin needed to capture it to enable his expedition to the Kantō.  At this time, Sano Masatsuna served as the lord of the castle.  Masatsuna was in a difficult situation caught in-between two major powers, namely, Uesugi Kenshin of Echigo and Hōjō Ujiyasu of Sagami.  To ensure the survival of his clan and the protection of the residents in his territory, Masatsuna sought to rely upon his military prowess and strategic acumen to overcome the turbulence of the times. 

Karasawayama Castle was a mountain stronghold counted among a group of key castles known as the Seven Famed Castles of the Kantō (with the others being Kawagoe, Oshi, Mayabashi (Maebashi), Nitta-Kanayama, Utsunomiya, and Taki castles).  Kenshin’s forces struggled in their attempts to capture Karasawayama Castle.  As a result, it was called the best mountain fortress in the Kantō.  While holed-up in the castle, Masatsuna repelled numerous assaults by the Uesugi army and then surrendered.  After the Uesugi army departed to Echigo, the Hōjō army attacked whereupon Masatsuna surrendered in turn to the Hōjō.  This led to a subsequent assault by the Uesugi army whereby he surrendered again to the Uesugi.  This approach reflected Masatsuna’s ability to adapt to the changing circumstances in an effort to survive.  While many sengoku daimyō were decimated in the Sengoku period, the Sano clan persisted through the wit of Masatsuna and the robust features of Karasawayama Castle.

Course of events

Battle in the second month of Eiroku 3 (1560)

Under another theory, this occurred in Eiroku 2 (1559).  Over the course of approximately ten battles at Karasawayama Castle, this is the only instance when Masatsuna and Kenshin joined forces to fight against the Hōjō.  Hōjō Ujimasa (the son of Hōjō Ujiyasu) led an army of 30,000 soldiers to attack Karasawayama Castle.  While fighting back, Masatsuna appealed to Kenshin for support.  Kenshin, with a smaller force, defeated the Hōjō army.  It is noted, however, that this battle may have been fabricated.

Battle in the twelfth month of Eiroku 4 (1561)

In the third month of 1561, Kenshin, accompanied by Masatsuna and others, surrounded the base of Ujiyasu at Odawara Castle in Sagami Province.  Although Ujiyasu faced a predicament, he held the castle and the Uesugi army withdrew to Echigo.  After the departure of the Uesugi army, Ujiyasu commenced a counterattacked and the Hōjō bore down on Karasawayama Castle.  Kenshin, however, could not spare reinforcements for Masatsuna while engaged in a dire battle against Takeda Shingen at Kawanakajima in Shinano Province.  Isolated, Masatsuna surrendered to Ujiyasu which Kenshin viewed as an act of betrayal and attacked but Karasawayama was a stronghold and owing to the arrival of winter weather Kenshin pulled back his forces.

Battle in the third month of Eiroku 5 (1562)

After spending the new year at Mayabashi Castle in Kōzuke, in the third month of 1562, Kenshin attacked Karasawayama Castle.  He could not, however, topple the mountain stronghold and pulled back his forces again.  After having successfully repelled the Uesugi army two years in a row, Masatsuna garnered attention among the populace for his military prowess.  Thereafter, Jinbō Nagamoto rebelled in Etchū so Kenshin was compelled to dispatch his army to Etchū to counter the rebellion.  The absence of the Uesugi provided an opening for the Hōjō to regain their power in the Kantō.

Battle in the fourth month of Eiroku 6 (1563)

In the second month of 1563, Ujiyasu, with reinforcements from Shingen, attacked and toppled Matsuyama Castle, the most important base for the Uesugi in Musashi Province.  Kenshin rapidly returned from Etchū to Echigo, and after traversing the snow-covered Mikuni Pass, headed toward the Kantō but did not arrive in time.  While away from the Kantō, many other castles in the Kantō defected to the Hōjō so Kenshin launched a series of assaults against these sites to force their surrender.  In front of this display of power by Kenshin, Masatsuna reluctantly surrendered and vacated Karasawayama Castle.  From the winter of 1563 to the following spring, Kenshin forced the surrender and turn-over of numerous castles including Kisai and Oshi castles in Musashi, Karasawayama and Gion (Oyama) castles in Shimotsuke, Koga and Yūki in Shimōsa, and Oda in Hitachi.

Battle in the second month of Eiroku 7 (1564)

In the second month of 1564, after Kenshin departed from Shimotsuke, Masatsuna rebelled again.  Karasawayama Castle was in a vital location to control the route for the Uesugi army to march from Mayabashi Castle in Kōzuke to Koga Castle (the Koga palace) in the central portion of the Kantō.  Repeated rebellions by Masatsuna caused major troubles for Kenshin.  Out of all of the battles between Kenshin and Masatsuna, this was the most violent.  The Uesugi mounted a ferocious assault, but the Sano army firmly resisted.  Karasawayama was situated atop a steep mountain with plentiful access to water so even Kenshin could not easily topple the stronghold.

At this time, Masatsuna’s reliable ally, the Hōjō clan, were engaged in battle against Satomi Yoshitaka of Awa at Kōnodai in Shimōsa Province so could not spare reinforcements.  Isolated and without support, it became difficult for Masatsuna to maintain a defense while the Uesugi army captured the outer citadels of the castle and approached the keep.  Following the advice of Satake Yoshiaki of Hitachi and Utsunomiya Hirotsuna of Shimotsuke, Masatsuna finally surrendered.  Yoshiaki and Hirotsuna pleaded with Kenshin to spare the life of Masatsuna whereupon Kenshin consented.  Later, Saitō Tomonobu, Yoshie Kagesuke, and Irobe Katsunaga (a member of the Agakita Group) were awarded certificates by Kenshin for their valor during this battle.

Battle in the tenth month of Eiroku 7 (1564)

In the eighth month, while Kenshin was preoccupied with his fifth battle against Shingen at Kawanakajima, Ujiyasu (who was allied with Shingen) sent his army again to the northern Kantō, threatening Karasawayama Castle.  Masatsuna submitted to the pressure by abandoning the Uesugi again.  This invited another attack by the Uesugi army.  In the tenth month, as Kenshin bore down on Karasawayama Castle, Masatsuna surrendered.  Kenshin took hostages from Masatsuna and returned to Echigo.

Battle in the second month of Eiroku 10 (1567)

Owing to the hostages tendered after the prior attack, and the fact that the Hōjō directed their primary forces toward an attack on the Satomi clan of Awa Province, Masatsuna did not defect from Kenshin for a while.  Kenshin, however, was confronted with conflict on three sides, including against the Takeda in western Kōzuke and northern Shinano, against the Hōjō across the Kantō, and against the Ikkō-ikk (followers of the Ikkō sect affiliated with the Ishiyama-Hongan Temple) in Etchū.  In 1566, after Kenshin failed in attempting to capture Usui Castle in Shimōsa and Wada Castle in Kōzuke, numerous daimyō in the Kantō defected to the Hōjō and the Takeda.  As the power of the Hōjō extended again to Shimotsuke, Masatsuna switched his allegiance again from the Uesugi to the Hōjō.  In the second month of 1567, Kenshin assaulted Karasawayama Castle, but struggled in the absence of reinforcements from other daimyō in the Kantō.  As the cold and snow of winter set in, Kenshin retreated with his forces to wait until the spring.

Battle in the third month of Eiroku 10 (1567)

Once the melting snow enabled the Uesugi army to storm Karasawayama Castle, the Sano army was forced to surrender.  Notwithstanding number rebellions, Kenshin spared the life of Masatsuna.  Despite the recapture of Karasawayama Castle, in this same year, Hōjō Takahiro defected to the Hōjō clan.  Takahiro was the chamberlain of Mayabashi Castle which served as the most important location in the Kantō for the Uesugi.  This made it likely that Kenshin would lose his authority as the deputy shōgun of the Kantō.  Thereafter, fissures occurred in the alliance between Shingen and Ujiyasu who jointly fought against Kenshin.  The two parties fiercely opposed one another over the issue of the Imagawa clan of Suruga.  Ujiyasu appealed to Kenshin for a reconciliation.  Kenshin responded by entering into the kōsō dōmei, or Alliance between Echigo and Sagami, bringing to an end for a while conflict between the Uesugi and the Hōjō in the Kantō.

Battle in the first month of Genki 1 (1570)

In the first month of Genki 1 (1570), after another betrayal by Masatsuna, Kenshin approached Karasawayama Castle with the intention of subduing him but the winter weather rendered it impossible to assault the castle so he pulled back his forces.

In 1574, Masatsuna died and was succeeded by his lineal heir, Sano Munetsuna.  Around this time, the alliance between the Uesugi and Hōjō clans was already broken, but by allying with the Satake clan, Munetsuna stood in opposition to the Uesugi and Hōjō.  In the Edo period, the castle was abandoned.