Mogami clan
were Japanese daimyōs, and were a branch of the Ashikaga family. In the Sengoku period, they were the Sengoku daimyōs who ruled Dewa Province which is now Yamagata Prefecture and part of Akita Prefecture. The Mogami clan is derived from the Shiba clan that was a branch of the Ashikaga clan. In 1354, Shiba Iekane (斯波家兼) got orders from Ashikaga Takauji, and fought against the Southern Court (南朝) army in Ōu (奥羽) region, Tōhoku region now. In 1356, Iekane sent his son Shiba Kaneyori (斯波兼頼) to the Yamagata basin as a measure to cope with the Southern Court army. Kaneyori built Yamagata Castle in about 1360, and won against the Southern Court army in 1367. After that, he settled there and took the name "Mogami", from the town in Dewa Province. This is the origin of the Mogami clan. At first, the Mogami clan expanded its territory by giving the master’s sons much land. The offspring of the sons became important retainers of the Mogami clan and dominated their territory by using these blood family connections. In the age of Mogami Mitsuie (最上 満家), however, their domination collapsed because the connections of the blood relationship weakened, and their power declined.