Giddianhi suggests that the only hope for the Nephites is to submit to him and his people. That would avoid warfare and the death of many. That part was certainly true, but it would also mean the end of the Nephites. Part of the conditions would be that they “unite with [the Gadiantons] and become acquainted with [their] secret works, and become [their] brethren that [the Nephites] may be like unto [the Gadiantons].
The stick after this carrot was that it was going to happen either way. If the Nephites did not submit, it would happen by force of arms.