There are several aspects of Ammoron's letter which must have angered Moroni. Ammoron's use of traditional Lamanite rhetoric about the right to rule must have been particularly infuriating. What did Ammoron care about Lamanite claims to governmental authority? He was a descendant of Zoram (v. 23). It wasn't his ancestors who were "wronged." He and his brother Amalickiah had become Lamanites not to preserve these ancient claims but to stake their own claims over the Nephites. Moroni, of course, recognized this and became even more angry, because he knew that Ammoron had a perfect knowledge of his fraud (Alma 55:1).
"Ammoron referred, of course, to Laman's complaint that Nephi 'thinks to rule over us,' when Laman himself claimed the right of rulership. 'We will not have him to be our ruler; for it belongs unto us, who are the elder brethren, to rule over this people' ("2 Ne. 5:32 Nephi 5:3). Ammoron represents the war as a continuation of an ancient feud between the two sets of brothers in Lehi's family. That hardly makes sense to us. Would countless thousands of men hundreds of years later throw themselves into battle simply to reclaim an ancient right? It is all the more puzzling because after the landing in America, Nephi and his descendants made no claims that we know of to rule the Lamanites. Quite to the contrary, Nephi withdrew from the site of the first landing by command of the Lord, leaving the area to his brothers (2 Nephi 5:5- 7). The first King Mosiah also withdrew by command of the Lord (cf. "Omni 1:12"Omni 1:13Omni 1:12-13), pulling back from the Lamanites and not forcing his rule on them. Until near the end, the Nephites never fought aggressive wars. The Lamanites were the ones to attack, not the Nephites." (John M. Lundquist and Stephen D. Ricks, eds., By Study and Also by Faith: Essays in Honor of Hugh W. Nibley on the Occasion of His Eightieth Birthday, 27 March 1990, 2: 54)