Western Yan
In 391, an incident that would have terrible consequences occurred to lead to the break of relations between Later Yan and Northern Wei. That year, Tuoba Gui sent his brother Tuoba Gu (拓拔觚) to Later Yan to offer tribute, and Murong Chui's sons detained Tuoba Gu and ordered Tuoba Gui to offer horses to trade for Tuoba Gu's freedom. Tuoba Gui refused and broke off relations with Later Yan, instead entering into an alliance with Western Yan.