We first meet the Amalekites in Alma 21:1-4. We find them in Lamanite country, but distinguished among the Lamanites by different name. The uniqueness of their name does not owe to a city, because their city (along with the Amulonites) was called Jerusalem. This tells us that they were a distinct body of people that had some uniting factor that wasn’t the city to which they belonged. We also learn that they were of the order of Nehor, which appears to be a religion that specifically derives from Nephite rather than more pure Lamanite religion. We have therefore suggested that the Amalekites were apostate Nephites, and that they have become Lamanites in the same way that the Zoramites have. This is confirmed in verse 13 below. We also saw in chapter 21 that they were very resistant to the teachings of Aaron and his brethren. This is consistent with the description in this verse.
What we have now is a force that is at least led by those who have personal ideological hatred for the Nephites that is more recent that that of the Lamanites at large. There is much more in this battle than simply a desire for territory or tribute. There is a class of ideas, a class of perceived rights, and the unique hatred that seems to come when one actively turns against an old way.