1589: Battle of Suriagehara and Rising Tensions in the Northern Provinces
Date Masamune defeated the Ashina at Suriagehara and captured Kurokawa Castle in Aizu. The balance of power in the north collapsed, heightening tensions that would lead to the Odawara Campaign the next year and the Pacification of Oshu the following year. Meanwhile, the Toyotomi regime advanced land surveys (kenchi) and central control.
Events this year
Month 6
Date Masamune defeated the forces of Ashina Yoshihiro at Suriagehara and subsequently entered Kurokawa Castle, taking control of Aizu.
See this battle in detail →Sources 福島県「県のすがた 中世」／猪苗代町「猪苗代城址と鶴峰城址（亀ヶ城公園）」／磐梯町「まちの歴史」
Month 8
Toyotomi Hideyoshi conducted a cadastral survey of Mino Province using uniform standards without distinguishing between direct holdings and daimyō domains, implementing policy to standardize military obligations and stipends nationwide.
Month 10
Inomata Norinao, the Later Hōjō castellan of Numata, seized Nagurumi Castle, which Toyotomi Hideyoshi's settlement had assigned to the Sanada.
11/24
Toyotomi Hideyoshi treated the seizure of Nagurumi Castle as a violation of his peace order and issued a declaration of war to Hōjō Ujinao.
The Later Hōjō strengthened Yamanaka Castle against an anticipated conflict with Toyotomi Hideyoshi, including the addition of the Daisaki outer enclosure.