Throughout scriptural history, we read about lineages and genealogies, whether in the Old Testament or in the New Testament. It was evidently customary for the nations of Israel to recognize who was the son of who as far back as tradition holds. This is how we learn in the first chapter of Matthew of Jesus Christ’s birthright to the throne of David, had He chosen to claim it.
When Mosiah discovered the land of Zarahemla, he learns of their genealogy after they had been taught the language of the Nephites and this is how they learned of their common history. There are examples in the Book of Mormon where someone recited his lineage before declaring his message. I believe that Ammon, the eldest son of King Mosiah, was being modest in his record keeping and left out a few parts. I think his introduction to the Lamanite king was more ceremonial than we read about.
I believe it went something like this: Ammon is brought bound before the king and he bows before Lamoni, recites his lineage as it is customary in the land. “Behold, O king, I am Ammon from the land of Zarahemla. I am the son of Mosiah, who is the son of Benjamin, who is the son of Mosiah…who was the son of Lehi who came out of Jerusalem during the reign of King Zedekiah.” And thus we discover that Lamoni was a descendant of Ishmael. Lamoni, the son of the king over all the Lamanites in the land of Ishmael was not ignorant of who the king of the Nephites in Zarahemla was and that before him knelt the heir to the throne in Zarahemla. Lamoni must have thought, “What does the prince of the Nephites want to do with us?”
Alma 17:22 And the king inquired of Ammon if it were his desire to dwell in the land among the Lamanites, or among his people.
23 And Ammon said unto him: Yea, I desire to dwell among this people for a time; yea, and perhaps until the day I die.
Lamoni, awestruck, was impressed–so impressed that he has Ammon’s bands removed.
24 And it came to pass that king Lamoni was much pleased with Ammon, and caused that his bands should be loosed; and he would that Ammon should take one of his daughters to wife.
I don’t think Lamoni was so intent on uniting kingdoms as he was simply wishing to honor the young prince in return. But Ammon politely declined, either because he was already married, perhaps with children back in Zarahemla, or his mind was otherwise simply single in purpose. His only desire was to serve and not rule. And he became King Lamoni’s servant by tending his flocks of sheep. What a fitting task for one who became a shepherd of a Lamanite nation. By the time he had proven himself a strong and loyal servant, his strength and royalty had been acknowledged and recognized:
Alma 18:13 And one of the king’s servants said unto him, Rabbanah, which is, being interpreted, powerful or great king, considering their kings to be powerful; and thus he said unto him: Rabbanah, the king desireth thee to stay.
“Ammon and Lamoni” by Joseph F. Brickley:
I believe it is reasonable to conclude that Ammon had indeed remained with this people after having served them for fourteen years in their land, even long after having brought them back to the land of Zarahemla to inherit the land of Jershon and and lived with them, becoming their high priest. If he was still alive when they migrated north after the civil wars, it is possible that he and his family departed with them:
Helaman 3:12 And it came to pass that there were many of the people of Ammon, who were Lamanites by birth, did also go forth into this land.