The descent of the resurrected Jesus who will come to Nephi’s descendants will usher in a period of righteousness. The time period is emphasized by a parallel phrasing that provides an emphasis by the number used: three generations pass away in righteousness, the fourth generation who passed away in righteousness.
After the passing of the fourth generation, then the angel shows Nephi that wars begin. The vision of wars is clearly contrasted to the time of righteousness, but it isn’t directly tied to a period of peace. That is, we get the antithetical parallel of righteousness and war, not the more expected set of peace and war.
If we remember the nature of the promise of the land, it is that they prosper according to righteousness. Therefore, while peace and war might be a more direct literary set, contrasting righteousness and war is completely appropriate according to the promise of the land given to both Lehi and Nephi.