Collapse in the Fifth Month of Daiei
The Collapse in the Fifth Month of Daiei (Daiei no satsuki kuzure) occurred in the spring of Daiei 4 (1524) and concerns the advance by Amago Tsunehisa, the daimyō and military governor of Izumo Province, into neighboring Hōki Province.
Beginning in the Eishō era (1504 to 1521), Tsunehisa intervened in an internal struggle within the Yamana clan, the military governors of Hōki. Yamana Sumiyuki inherited from his father, Yamana Yukihiro, a campaign to oppose the military governor. Tsunehisa then supported Sumiyuki to become the military governor in lieu of Yamana Hisayuki (Sumiyuki’s cousin). Despite his title, Sumiyuki was essentially a puppet of Tsunehisa, while Tsunehisa sent his grandson, Amago Haruhisa, to serve as the vice-governor in the Hino District of Hōki under the direct control of the Amago clan.
Through these steps, the Amago established their governance of western Hōki. The Amago pacified residents of the Hino District in the southern portion of western Hōki. While imposing their control over Hino, the Amago expelled kokujin, or local families of influence, from the northern portion of western Hōki as a means to expand their own influence. At this time, their governance was limited to western Hōki. From the early Tenmon era (1532-1555), the Amago began to advance into eastern Hōki, encountering resistance from locals opposed to their rule supported by families from Mimasaka Province. Owing to dissatisfaction with control by the Amago over the family of the military governor, Yamana Sumiyuki joined the resistance. However, the death of Sumiyuki in 1533 marked a decline in the strength of the resistance, enabling the Amago to consolidate control of eastern Hōki around 1540.
Locals who fell under the command of the Amago included influential clans from the Hino District (the Hino, the Hino-Yamana, and the Hachitsuka), along with the Kawaoka, the Katayama, the Fukuyori, the Ogamo, and Nanjō clans. Meanwhile, some families fled the province, including the Yamada, the Yukimatsu and the Murakami, primarily heading to the Ōuchi and Tajima-Yamana clans for protection. Although initially aligned with the Amago, in 1546, the Nanjō responded to an appeal from Takeda Kuninobu to abandon the Amago and depart from Ueshi Castle in eastern Hōki. Also in 1546, Nanjō Sōshō, lord of Ueshi Castle, initiated the Battle of Hashizugawa with the support of the Tajima-Yamana, and served as a pillar of the resistance against the Amago. Thereafter, many other kokujin of eastern Hōki recovered their former territories with the support of the Mōri clan,
Although, for a period of time, the Amago had established their governance over the entire province of Hōki, their control over the eastern portion was tenuous. Amago Tsunehisa, the head of the Amago clan and a renowned military strategist, died in 1541. Two years later, the Nanjō supported the allied forces of the Ōuchi and the Mōri in an attack against Gassantoda Castle in Iwami Province. The elite fighting forces of the Amago known as the Shingūtō defended against the attack, but it served as a forewarning of deepening challenges to their governance. In 1552, Amago Haruhisa became the military governor of Hōki, but his control did not extend to the entire province. The Amago actively exercised governance of eastern Hōki and Mimasaka, while, in the western portions, local families such as the Nanjō exercised discretionary authority under the general governance of the Amago. Following the death of Haruhisa in 1561, the Amago and Mōri entered into settlement negotiations. Beginning with Honjō Tsunemitsu, lord of Yamabuki Castle in Iwami, kokujin formerly under the control of the Amago submitted to the Mōri, while other clans recovered their former territories with the support of the Mōri. These developments led to the expulsion of the Amago from western Hōki. Thereafter, the combined forces of the Mōri and Mimura clans battled against the Amago throughout eastern Hōki and Mimasaka.