Koshamain's War

Koshamain's War (コシャマインの戦い, Koshamain no tatakai) was an armed struggle between the Ainu and Wajin that took place on the Oshima Peninsula of southern Hokkaidō, Japan, between 1457 and 1458. Escalating out of a dispute over the purchase of a knife, Koshamain and his followers sacked twelve forts in southern Ezo (道南十二館), before being overcome by superior forces under Takeda Nobuhiro. The principal record of the conflict is the Shinra no Kiroku, written in 1646. However, as it was written approximately 200 years after the events, historians note that its contents require critical verification. The conflict was a pivotal event in the history of the region, leading to the consolidation of Japanese power and the eventual formation of the Matsumae Domain.