In Alma 43:5 we find that "the Lamanites came with their thousands; and they came into the land of Antionum, which is the land of the Zoramites." Brant Gardner notes that this is not simply a rebellion of Zoramites in Antionum, but the war will encompass part of the military might of the Lamanites. This process of combining forces with those of another city state was a common practice in Mesoamerican warfare. Indeed, part of the continued success of a large hegemony of city states was the ability to muster armies from a much larger land than that of the central city which was politically dominant. This became particularly true of the Aztec empire. The larger they became, the more difficult it was to overthrow them because of their ability to muster and provision large armies at distant locations.
It is interesting to note here that the presence of the Lamanites in Antionum is precisely the fear which led Alma to begin preaching to the Zoramites in the first place (see Alma 31:3-6). Antionum held a very strategic position on the eastern flank of the land of Zarahemla, and opening Antionum as a support base for Lamanite military action opened a major breach in the geographic defenses of Zarahemla. [Brant Gardner, "Book of Mormon Commentary," at [http://www.frontpage2k.nmia.com/~nahualli/LDStopics/Alma/] Alma43.htm, pp. 7-8]