Helaman 11:20

And thus it did come to pass that the people of Nephi began to prosper again in the land, and began to build up their waste places, and began to multiply and spread, even until they did cover the whole face of the land, both on the northward and on the southward, from the sea west, to the sea east.

The Nephites started doing well again in the land. They rebuilt the places that had been destroyed. They had more and more children. They spread out until they covered the whole land. They lived in the north and the south. They lived from the west sea to the east sea.

So the people of Nephi began to thrive again. They rebuilt what had been destroyed and started to grow and spread until they covered the whole land—north and south, from the west sea to the east sea.