Of course there is peace in the land of the Lamanites are righteous, because there is no conflict between them and the Nephites. While this is Mormon’s implication, the historical reality would have been different from this implication. There were certainly many Lamanites who were converted to the gospel, but it is also certain that not all of the Lamanites were converted to the gospel. The peace in the land coincides with this missionary effort of the Lamanites, but is not likely to have been caused by it. What we learn in the next verse is that there is a general economic prosperity, and when everyone is equally sharing in economic prosperity there is little pressure for wars of expansion.