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」
After Kenshin's death, Kagekatsu secured control of Kasugayama Castle's central stronghold. Kagetora established his base at Otate and opposed him. Echigo's regional lords divided their allegiances and the domain descended into civil war.
Sources 新潟県上越地域振興局「上越妙高 山城マップ」
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」
11/6
Oda's large Ataka warships commanded by Kuki Yoshitaka defeated the Mōri fleet and cut off seaborne supply routes to Ishiyama Honganji.
Sources 鳥羽市「九鬼嘉隆（人物概要）」
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.
11/24
Nakagawa Kiyohide, who had been besieged under Araki Murashige, expelled Murashige's supporters Ishida Iyo and Watanabe Kantayū and surrendered to Oda Nobunaga.
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」
When Araki Murashige defected from Oda Nobunaga, Takayama came under attack from the Oda forces but surrendered and was pardoned, retaining his position as lord of Takatsuki Castle.