1578: The Sudden Death of Uesugi Kenshin and Araki Murashige's Revolt
In March, Uesugi Kenshin died suddenly without naming an heir, and his adopted sons Kagekatsu and Kagetora plunged Echigo into the succession struggle known as the Otate no Ran. In the Kinai region, Nobunaga's trusted retainer Araki Murashige unexpectedly defected to the Mōri-Hongan-ji side and fortified himself in Arioka Castle, threatening Nobunaga's hold on Settsu.
Events this year
Month 3
Bessho Nagaharu of Miki Castle broke with the Oda and aligned with the Mōri, prompting Hashiba Hideyoshi to begin the siege of Miki.
See this battle in detail →Sources 三木市「三木合戦とは【豊臣兄弟と三木】」／三木市「三木城跡及び付城跡・土塁（国指定史跡）」／三木市「三木合戦の史跡・スポット」
Month 7
Oda Nobunaga's heir Nobutada joined the Miki campaign and strengthened the siege by constructing forts, including the hilltop fort at Hiraiyama that served as Hashiba Hideyoshi's headquarters.
See this battle in detail →Sources 三木市「三木合戦とは【豊臣兄弟と三木】」／三木市「三木城跡及び付城跡・土塁（国指定史跡）」／三木市「三木合戦の史跡・スポット」
11/12
Ōtomo Sōrin's army, which had marched to recover Hyūga, suffered a major defeat at Takajō and Mimikawa against the forces of Shimazu Yoshihisa and Yoshihiro. Shimazu control over Hyūga was consolidated, and Ōtomo's dominance was lost.
Uesugi Kenshin died suddenly without leaving a surviving document that clearly named his successor. Uesugi Kagekatsu secured the core of Kasugayama Castle, and conflict with Uesugi Kagetora's faction developed into the Otate civil war.
Sources 上越市「春日山城跡」／南魚沼市「坂戸城跡」／新潟県「関興寺」