Jacob does not explain why the Nephite repentance led them to seek a similar repentance among the Lamanites. If Sherem had truly come from a Lamanite community, that provides the explanation for his understanding of the scriptures, the reason he was so against the atoning Messiah, and thus turning to the Lamanites as a result. If Sherem came from the Lamanites and he had repented, then thinking the Lamanites might repent would have been reasonable.
Nevertheless, the hatred was too strong, and the relationship with the Lamanites was not one of peace, but rather of war. Neither Nephi nor Jacob spend any time discussing wars in their small plate record. We must assume that they were chronicled on the large plates and neither Nephi nor Jacob saw reason to record them on the small plates that had a different purpose.
Jacob notes that they fortified themselves against the Lamanites, and “became as yet, conquerors of their enemies.” That might suggest Nephite wars of conquest, but is more likely a translation term that simply indicated that they had defeated the Lamanites in battle. Subsequent writers will note that they did often defeat, or conquer, their enemies, but it is never said that they acquired territory through that method, which is the typical understanding of the word conquer.