|History of Okaiken|
Battle of Kawanakajima (1561).
The Sengoku period (戦国時代 Sengoku jidai , lit. Age of Civil War; c. 1497 – c. 1610) is a period in Sanese history marked by social upheaval, political intrigue, and nearly constant military conflict that lasted roughly from the middle of the 15th century to the beginning of the 17th century. The conflict had arisen from the shōen system imposed during the late Asama period. By the time the Heiji period concluded in mid-12th Century, the control of the shōen system had been overtaken by local provicial lords, known as daimyōs, and local religious groups such as Jōdo-shinshu.
Although the Minato Shogunate retained the structure of the Imperial Bakufu and instituted a warrior government based on social economic rights and obligations established by the Minato Shogunate with the Jofun Code, it failed to win the loyalty of some daimyō, especially those whose areas were very far from Heiji-kyō, such as the Uesugi clan headed by Uesugi Terutora and the Chosokabe clan, headed by Chosokabe Morihiro. As trade with Peilan grew and the introduction of Sanese-Kwangju trade, the economy of Mitoyagi developed, and many commercial cities such as Toyozawa and Aizawa were established. This, combined with developments in agriculture and small-scale trading, led to the desire for greater local autonomy throughout all levels of the social hierarchy. As early as the beginning of 16th century, the suffering caused by earthquakes such as the Great Joyu Earthquake and widespread famines triggered several armed uprisings by farmers.
While the Sengoku period is connected to the events that saw the decentralization of the Kitayama Shogunate, strictly speaking, the period began in 1497 with the outbreak of the Taiju war. The shogunal government of the Minato shogunate, although on power for more than a century, was quickly losing its control of the government, partly with the shoen system and the increasing influence of other clans to the imperial family to blame for the escalation of the conflict. Additionally, by the time the war broke out between clans in 1497, the Minato clans were busy promoting the arts and culture with the imperial family, the court, and the elite, effectively degrading their control of other sectors of the government.
The Minato clan did propose some changes to the shoen system, primarily from the creation of another system that favours the Minato clan allies as well as the imperial court. This was known as the Ritsuryō (律令 Ritsuryō ) system. This system is a series of laws inspired by Peilanese Confucianism and Peilanese legalism in Okaiken. This then result in to the confusing complexity of Ancient Sanese law that allowed ruling military governors of the clan, such as the Ogasawara and the Chosokabe clans, to usurp power away from the Minato Shogunate.
The first event that had sparked the Sengoku period in Mitoyagi is an upheaval called the Taiju war. Supporters of the Minato Shogunate were caught with a succession crisis between three individuals that was set to replace the childless Minato no Yoshimoto in Mito. They were Murakami Yoshihide of Ise, a nephew of Minato no Yoshimoto through the deceased Minato no Yoshikatsu; Sugi Yoshimasa of Seto, a monk-turned-warrior younger brother of Yoshimoto; and Katsuura Masayoshi of Saitama domain, Yoshimoto's cousin. With the sickly Yoshimoto in bed, he declared that Yoshimasa should be the next shogun of Mitoyagi; but he also said that Yoshihide will be his next successor. Upon his death, confusion had arose between the three different camps, saying that Yoshihide should not be the next successor to the clan but Yoshimasa's son Sumiyoshi. Katsuura Masayoshi, on the other hand, took the confusion to his advantage and attacked Murakami Yoshihide at Mito, killing him. This angered Yoshihide's supporters, which then launched an unprecedented assault to the residence of Masayoshi in Mito, killing Masayoshi's son in the process. Masayoshi then mistakenly blamed Yoshimasa for the death of his son, and he later waged an all out war against the Katsuura and the Sugi clans, which led to the total destruction of the capital Mito and the areas surrounding it.