against his rival Nanbu Nobunao which spread across Mutsu Province. Nobunao was backed by Toyotomi Hideyoshi, who along with Tokugawa Ieyasu sent a large army into the Tōhoku region in mid-1591 which quickly defeated the rebels. Hideyoshi's army arrived at Kunohe Castle in early September. Masazane was outnumbered and surrendered Kunohe Castle but he and the castle defenders were executed. The Kunohe rebellion was the final battle in Toyotomi Hideyoshi's campaigns during the Sengoku period and completed the unification of Japan. Korean campaign (1592–1598) Taikō The future stability of the Toyotomi dynasty after Hideyoshi's eventual death was put in doubt with the death of his son Tsurumatsu in September 1591. The three-year-old was his only child. When his half-brother Hidenaga died shortly after, Hideyoshi named his nephew Hidetsugu his heir, adopting him in January 1592. Hideyoshi resigned as kampaku to take the title of taikō (retired regent). Hidetsugu succeeded him as kampaku. With Hideyoshi's health beginning to falter, but still yearning for some accomplishment to solidify his legacy, he adopted Oda Nobunaga's dream of a Japanese conquest of China and launched the conquest of the Ming dynasty by way of Korea (at the time known as Koryu or Joseon). Hideyoshi had been communicating with the Koreans since 1587 requesting unmolested passage into China. As an ally of Ming China, the Joseon government of the time at first refused talks entirely, and in April and July 1591 also refused demands that Japanese troops be allowed to march through Korea. The government of Joseon was concerned that allowing Japanese troops to march through Korea (Joseon) would mean that masses of Ming Chinese troops would battle Hideyoshi's troops on Korean soil before they could reach China, putting Korean security at risk. In August 1591, Hideyoshi ordered preparations for an invasion of Korea to begin. First campaign against Korea In the first campaign, Hideyoshi appointed Ukita Hideie as field marshal, and had him go to the Korean peninsula in April 1592. Konishi Yukinaga occupied Seoul, which was the capital of the Joseon dynasty of Korea, on June 19. After Seoul fell easily, Japanese commanders held a war council in June in Seoul and determined targets of subjugation called Hachidokuniwari (literally, dividing the country into eight routes). Each targeted province was attacked by one of the army's eight divisions: Pyeongan by the First Division led by Konishi Yukinaga. Hamgyong by the Second Division led by