Alma speaks with the spirit of prophecy and revelation in disclosing to the people that if they fail to repent, “after having had so much light” (verse 19), the Lamanites will come upon them to destroy them. That is exactly what comes to pass (see Alma 16:3, 10). That is also what eventually comes to pass for the entire Nephite nation, of which Ammonihah is merely the microcosm that presages the fall of the entire civilization through pride and iniquity.