It is not clear how much time passed between the resolution of the previous war and these new hostilities. “After many days” could mean anywhere from a few days to perhaps a few months. It was probably not as much as a year, since that time-unit would have been easier to note than “many days,” particularly since the large plates were apparently kept by years. (See commentary accompanying Mosiah 6:7.)
Thus, it seems likely that the increase in hostilities is relatively close in time and, therefore, likely to be based on the same reasons. Since the previous conflict regarded the oath, what is creating this conflict? Mormon does not say. I speculate, however, that while the Lamanites recognized that the Limhites were probably not guilty of oath-breaking by abducting the Lamanite young women, the issue was still unresolved because it had not been determined that Noah’s priests were the real culprits. In this situation, the treaty had been officially reinstated, but individual Lamanites no doubt still harbored suspicious about the Limhites’ innocence. After all, the priests of Noah had come from this city. If they believed that the Limhites were indeed guilty (if only by association), the resumption of hostilities is understandable.