It is not surprising that the Lamanites repelled their attack with considerable loss of life, forcing them to retreat to their city. Mosiah 19:2 explained that the army was greatly reduced during Noah’s destruction. Alma’s disciples almost certainly included a number of able-bodied men. And finally, despite the successful ambush, no doubt the Limhites, already outnumbered two to one (Mosiah 20:11), had suffered casualties. With the Lamanites surrounding the Limhites geographically, with clear numerical superiority, and with an expectation of violence (and perhaps even the hope of provoking it) the battle to which the Limhites sallied forth was doomed from the start.
As an insight into Mesoamerican culture, however, the battle ends when the defeated Limhites retreat to their city. There is no further attack. The tribute function was still important, and the Lamanites’ military goal was no doubt to suppress rebels and compel them to accept their tributary status. While Western history might predict retaliatory destruction, it did not happen.
Geography: The Lamanites are able to surround the Limhites, and apparently all Limhite action came from a single location, presumably the city of Lehi-Nephi. Zeniff was also granted the land of Shilom (Mosiah 9:6) and Noah had a building project in Shilom (Mosiah 10:13), but Limhi’s record does not mention Shilom. Somewhere, Shilom passed back into Lamanite hands—perhaps at the time of Noah. Perhaps it was the site of a separate battle, perhaps the one that resulted in the reduction of the Nephite army (Mosiah 19:2). In any case, Shilom is lost, and Lehi-Nephi is completely surrounded. It is to that one remaining city that Ammon will come.