When Masamune DATE intervened in an internal disturbance of the Osaki clan by using force, which is called the Battle of Osaki in January and February 1588, since the Osaki family was the head house of the Mogami family as well as the family home of Yoshiaki's lawful wife, Yoshiaki sent reinforcements to Osaki's territory.
翌天正16年（1588年）1月、最上家の本家にあたり正室の実家でもある大崎氏の内紛に伊達政宗が武力介入すると（大崎合戦）、義光は政宗を討つべく大崎領に援軍を派遣した。