The righteousness of the people had allowed them to defeat the Gadiantons, recognizing that Jehovah was with them. The promise of the land protected them. When the war was over, they did not immediately forget their lessons, and continued to obey the commandments.
According to the promise of the land, they began to prosper. Their prosperity was manifest in the improvements in cities and in roads. This peace continued for two years from the date at the beginning of the chapter. However, as noted in the comments on verses 1-3 of this chapter, Mormon had repeated information that actually belonged in the twenty-second year. Therefore, this time of peace lasted, for the Nephites, a remarkable six years.