# Hōjō Sōun's seizure of Izu
Hōjō Sōun's seizure of Izu (北条早雲の伊豆討入り) was the campaign by which the warlord Ise Shinkurō Nagauji, later known as [Hōjō Sōun](https://www.edgepedia.org/hojo-soun) (born 1432 by the older theory, 1456 by more recent theories; died 1519), took over Izu Province, ending with the fall of Fukane Castle in the eighth month of Meiō 7 (1498).[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [2](https://toukenza.jp/en/events/hojo-soun-izu-unification) The sides were Sōun against Chachamaru, the head of a cadet branch of the Ashikaga shogunal house.[4](https://www.touken-world.jp/dtl/izu/) • [5](https://sengoku-his.com/427) • [6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html) The campaign ended with Sōun in control of all Izu, while Chachamaru's own fate is reported differently.[3](https://history.kaisetsuvoice.com/Sengoku02.html) • [8](https://love-japanese-history.com/jinbutu-houjyousouun/)
| Key fact | Detail |
|---|---|
| Place | Izu Province, at the Horigoe palace and Fukane (Fukune) Castle in southern Izu[2](https://toukenza.jp/en/events/hojo-soun-izu-unification) • [3](https://history.kaisetsuvoice.com/Sengoku02.html) |
| Sides | Ise Sōun with Imagawa and Ōgigayatsu Uesugi cooperation, versus Ashikaga Chachamaru of the Horigoe kubō[3](https://history.kaisetsuvoice.com/Sengoku02.html) • [5](https://sengoku-his.com/427) |
| Forces | About 500 men in the landing force: 200 of Sōun's own and 300 borrowed from Imagawa Ujichika[4](https://www.touken-world.jp/dtl/izu/) • [6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html) |
| Outcome | The Horigoe kubō line was destroyed; Sōun ruled all Izu from newly built Nirayama Castle[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [3](https://history.kaisetsuvoice.com/Sengoku02.html) |
| Consequence | Regarded as an opening act of the Sengoku age of gekokujō, and the foundation of the Later Hōjō house[3](https://history.kaisetsuvoice.com/Sengoku02.html) • [4](https://www.touken-world.jp/dtl/izu/) • [10](https://jref.com/articles/later-h%C5%8Dj%C5%8D-clan.377/) |
## Background and causes
Izu was the seat of the Horigoe kubō, a cadet branch of the Ashikaga shoguns.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [7](https://pastinpractice.com/articles/hojo-soun) The kubō Masatomo's first wife's son was Chachamaru; his second wife Enman'in bore Jundōji and a third son.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html)
The immediate cause was a succession struggle. Because Enman'in wanted her own son Jundōji as heir, she imprisoned Chachamaru on a trivial charge. When Masatomo died of illness in the fourth month of Entoku 3 (1491), Chachamaru escaped, killed Enman'in and Jundōji, and declared himself the second Horigoe kubō.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [5](https://sengoku-his.com/427) This made him an enemy of the new shogun: Enman'in was the real mother of [Ashikaga Yoshizumi](https://www.edgepedia.org/ashikaga-yoshizumi), and Yoshizumi ordered Imagawa Ujichika of Suruga to punish Chachamaru.[3](https://history.kaisetsuvoice.com/Sengoku02.html) • [6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html)
A wider political alignment gave the order force. In the fourth month of Meiō 2 (1493) the kanrei [Hosokawa Masamoto](https://www.edgepedia.org/hosokawa-masamoto) carried out a coup in Kyoto, deposing the tenth shogun Ashikaga Yoshiki (later Yoshitane) and installing Yoshizumi (Kiyōshō) as the eleventh shogun.[5](https://sengoku-his.com/427) • [6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html) Sōun, then based at Kokokuji Castle in Suruga as a relative and guardian of the young Imagawa Ujichika, acted as the Imagawa force's commander in the invasion.[7](https://pastinpractice.com/articles/hojo-soun) • [5](https://sengoku-his.com/427)
## Course of events
The landing and night attack, 1493. Sōun, based at Kokokuji Castle, borrowed troops from Imagawa Ujichika and with about 500 men made a night attack on the Horigoe palace.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) His own force was 200 men, with 300 borrowed from Ujichika.[4](https://www.touken-world.jp/dtl/izu/) • [6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html) The Ōgigayatsu Uesugi, with whom Sōun would later fight over Sagami, cooperated in the invasion.[5](https://sengoku-his.com/427) • [3](https://history.kaisetsuvoice.com/Sengoku02.html)
The fall of the Horigoe palace. The traditional account says Sōun destroyed Chachamaru within one month.
The siege of Fukane Castle, 1493–1498. In the eighth month of Meiō 7 (1498) the great Meiō Earthquake and tsunami of the 25th day of that month devastated southern Izu, destroying the castle's facilities and cutting its supply lines.[2](https://toukenza.jp/en/events/hojo-soun-izu-unification) • [8](https://love-japanese-history.com/jinbutu-houjyousouun/) In the eighth month of Meiō 7 (1498) Sōun attacked Fukane Castle, which fell, and he completed control of all Izu.[3](https://history.kaisetsuvoice.com/Sengoku02.html)
## Outcome and losses
The political life of the Horigoe kubō was certainly ended.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) Chachamaru's own fate is reported differently: he was killed at the palace, fled to nearby Moriyama and killed himself there, or escaped;[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) recent research has him cornered and taking his own life in Kai Province in the eighth month of Meiō 7 (1498);[5](https://sengoku-his.com/427) • [6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html) and a third account has him surrendering after the earthquake, taken captive and executed by Sōun.[2](https://toukenza.jp/en/events/hojo-soun-izu-unification)
## Consequences and political influence
Sōun built Nirayama Castle near the Horigoe palace and made it his residence, keeping it even after he later gained [Odawara Castle](https://www.edgepedia.org/odawara-castle) in Sagami.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [8](https://love-japanese-history.com/jinbutu-houjyousouun/) He then regulated his new domain. According to the Hōjō Godaiki he responded to a spreading epidemic in Izu by procuring medicine and reduced the land tax from five-parts-to-five (gokō gomin) to four-parts-to-six (shikō rokumin); the same source's claim that Izu was pacified in one month is an exaggeration, but its attention to civil administration is considered factual.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) He guaranteed the lands of those who joined him, forbade his soldiers' violence, and later ruled that collection orders without his sealed verdict (inpanjō) were invalid, stopping unlawful extraction by gun-dai and daikan.[4](https://www.touken-world.jp/dtl/izu/) • [8](https://love-japanese-history.com/jinbutu-houjyousouun/) No major revolt followed the pacification.[2](https://toukenza.jp/en/events/hojo-soun-izu-unification)
The seizure also marked an institutional shift. Sōun had acquired a province through his own military strength without dependence on shogunal sanction, a sign that shogunal authority had waned and that daimyo were developing independent power bases.[2](https://toukenza.jp/en/events/hojo-soun-izu-unification) Because Chachamaru, of the shogun's own cadet line, was destroyed by a local warlord, the Izu raid is called the opening arrow of gekokujō, the overthrow of superior by inferior that defines the Sengoku age.[4](https://www.touken-world.jp/dtl/izu/) • [3](https://history.kaisetsuvoice.com/Sengoku02.html) To legitimate the new name, the family's later head Ujitsuna was married to a descendant of the family that had controlled the previous warrior government, from whom the Hōjō name came.[9](https://journal.oraltradition.org/wp-content/uploads/files/articles/15ii/7_thornton.pdf) From this base the Ise, or Odawara, Hōjō went on to control Izu, Sagami, and most of Musashi.[9](https://journal.oraltradition.org/wp-content/uploads/files/articles/15ii/7_thornton.pdf)
## Historians' assessment
Two points of the traditional story have been revised. First, the date: older descriptions put the invasion in Entoku 3 (1491), but the Odawara city encyclopedia holds that Meiō 2 (1493) is more plausible, since 1491 is the year of Masatomo's death and of the deaths of Enman'in and Jundōji.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) Second, the character of the act: Sōun was once depicted as a lone upstart achieving gekokujō, but recent scholarship sees the invasion as coordinated with the bakufu, acting on Yoshizumi's order and in step with Hosokawa Masamoto's coup.[6](http://www4.tokai.or.jp/bajoushounen/kassen2018.html) • [5](https://sengoku-his.com/427) The pace of conquest has likewise been corrected: the one-month pacification of the Hōjō Godaiki is an exaggeration, and the campaign in fact ran from 1493 to 1498.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [2](https://toukenza.jp/en/events/hojo-soun-izu-unification) How Chachamaru died, and exactly where, the available accounts do not settle.[1](https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/) • [5](https://sengoku-his.com/427)
## References
1. 小田原市｜北条早雲の伊豆討入り: https://www.city.odawara.kanagawa.jp/encycl/neohojo5/003/
2. Hōjō Sōun's Unification of Izu: https://toukenza.jp/en/events/hojo-soun-izu-unification
3. 北条早雲（ニ）伊豆侵攻｜日本の歴史 解説音声つき: https://history.kaisetsuvoice.com/Sengoku02.html
4. 伊豆討ち入り古戦場：静岡県: https://www.touken-world.jp/dtl/izu/
5. 「伊豆討ち入り（1493年）」北条早雲が堀越御所を攻略し、伊豆国を制圧した真相とは | 戦国ヒストリー: https://sengoku-his.com/427
6. 合戦１ | １４９３年 堀越居館の戦い 北条早雲 ＶＳ 足利茶々丸: http://www4.tokai.or.jp/bajoushounen/kassen2018.html
7. Hōjō Sōun: The Real Start-Up Story of a Sengoku Warlord: https://pastinpractice.com/articles/hojo-soun
8. 【北条早雲（伊勢宗瑞）】一代で伊豆国・相模国を切り取った最初の戦国大名: https://love-japanese-history.com/jinbutu-houjyousouun/
9. Kōnodai senki: Traditional Narrative and Warrior Ideology in Sixteenth-Century Japan (Oral Tradition): https://journal.oraltradition.org/wp-content/uploads/files/articles/15ii/7_thornton.pdf
10. Later Hōjō Clan | Japan Reference: https://jref.com/articles/later-h%C5%8Dj%C5%8D-clan.377/
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*Topic: Encyclopedia › Society and history › History and archaeology › Asian history › Japan › Sengoku and Azuchi-Momoyama Japan (1467 to 1603) › Sengoku daimyo and figures*
*Initially written Sep 24, 2026 · Reviewed: Sep 30, 2026 · Edited: Sep 30, 2026; Oct 21, 2026; Oct 25, 2026 · Last review: Sep 30, 2026*
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