Ammon presents us with an unusual set of events without any comment. He is presented before the king, who asks if he desires to dwell among the Lamanites. Since Ammon did not arrive with an army, it was possible that there was a sincere desire to settle in the lands. Ammon commits to living among them, perhaps until he died. That didn’t happen, but Ammon was willing for it to happen.
Then things start to get interesting. King Lamoni agrees to let him live among his people and suggests that Ammon marry one of King Lamoni’s daughters. That quick offer requires some background to be believable. It is possible that Ammon also provided his genealogy. That would not have been unusual, and even though he and his brothers had declined the throne, they were still related to a Nephite king. Perhaps that was the reason that King Lamoni sought to create a tighter alliance by offering a daughter in marriage.
Also plausible is that King Lamoni understood that Ammon would become his son-in-law, and, therefore, under the will and power of Lamoni, with family obligations of obedience. It would have been an extension of the idea of the alliance, but would assure that the Nephite, who had no allegiance to any Lamanite, had an important tie to the king.