to intermarry between allied families
重縁を結ぶ - 斎藤和英大辞典
After the downfall of the Minamoto clan, the Ashikaga clan maintained a good, although subordinate, relationship with the Hojo clan, continuing to intermarry and being granted use of Chinese characters from the names of Hojo people.
源氏将軍家滅亡後も北条氏とは婚姻や偏諱を通じて良好な従属関係を維持してきた。 - Wikipedia日英京都関連文書対訳コーパス