After the death of the fifth shōgunAshikaga Yoshikazu in 1425, the fourth shōgunAshikaga Yoshimochi resumed his role as head of the shogunate. Yoshimochi had no other sons, nor did he name a successor before he himself died in 1428.
Yoshinori, who had been a Buddhist monk since the age of ten, became Sei-i Taishōgun on the day of Yoshimochi's death. From amongst the handful of possible Ashikaga candidates, his name was selected by the shogunal deputy (Kanrei), Hatakeyama Mitsuie, who drew lots in the sanctuary of Iwashimizu Hachiman Shrine in Kyoto; and it was believed that Hachiman's influence had affected this auspicious choice.
Significant events which shaped the period during which Yoshinori was shōgun:
1439 – Mochiuji commits suicide; dissatisfaction with Yoshinori grows.
1440 – Yasaka Pagoda at Hokanji in Kyoto re-constructed by Yoshinori.
1441 – Yoshinori grants Shimazu suzerainty over the Ryūkyū Islands; Akamatsu murders Yoshinori – Kakitsu Incident; Yamana kills Akamatsu.
Yoshinori strengthened the power of the shogunate by defeating Ashikaga Mochiuji in the Eikyo Rebellion of 1438. During the period, Chinese contacts were increased and Zen Buddhism gained influence, which had broad cultural consequences. For example, the Hon-dō or main hall at Ikkyu-ji is today the oldest standing Tang-style temple in the Yamashiro (southern Kyoto Prefecture) and Yamato (Nara Prefecture) Provinces. It was built in 1434 and was dedicated by Yoshinori.
In 1432, trade and diplomatic relations between Japan and China were restored. Both had been discontinued by Yoshimochi. The Chinese emperor reached out to Japan by sending a letter to the shogunate via the kingdom of the Ryūkyū Islands; Yoshinori responded favorably.
According to Mansai Jugo Nikki (満済准后日記), the system of the Tosen-bugyō (唐船奉行) was established in 1434 to mediate overseas trade. The functions of the Tosen-bugyō included: (1) defending trading ships in Japanese waters, (2) procuring export goods, (3) mediating between the Muromachi shogunate and shipping interests, and (4) managing record-keeping. It is significant that the Muromachi shogunate was the first to appoint the executive officers of the samurai class to high positions in its diplomatic bureaucracy. After Yoshinori's time, the totosen (渡唐船) (the fleet of ships going from Japan to Ming China) consisted of the ships belonging principally to three different kinds of owners: the Muromachi shōgun, temples, and the shugodaimyō.
Yoshinori was notorious for his oppressive measures and unpredictable dictatorial whims. Yoshinori was assassinated by the Akamatsu family of military governors who invited him to a Noh performance at their residence and assassinated him during the evening play. Yoshinori was 48 at the age of his assassination which was organized by Akamatsu Mitsusuke, who had learned that Yoshinori planned to bestow on a youthful male favorite three provinces belonging to Mitsusuke; shortly thereafter, it was determined that his 8-year-old son, Yoshikatsu, would become the new shōgun.
Although the Ashikaga line continued through this seventh shogun, the power of the shōguns gradually eroded and the shogunate fell into decline. The mere fact of that assassination and treason had become a reality served to undercut the previous military ethic of loyalty.
Eras of Yoshinori's bakufu
The years in which Yoshinori was shogun are more specifically identified by more than one era name or nengō.
^Titsingh, p. 340., p. 340, at Google Books; Screech, Timon. (2006). Secret Memoirs of the Shoguns: Isaac Titsingh and Japan, 1779–1822, p. 234 n.10; n.b., Yoshinori (b. 1394 – d. 1441) = 48yrs. and Yoshikatsu (b. 1434 – d. 1443) = 8yrs. In this period, "children were considered one year old at birth and became two the following New Year's Day; and all people advanced a year that day, not on their actual birthday."