Mormon had already recorded Nephi2’s departure and disappearance (3 Ne. 1:2) but repeats it here for its literary effect. Righteousness has, symbolically, departed from the land.
3 Nephi 2:10
10 And it came to pass that the people did still remain in wickedness, notwithstanding the much preaching and prophesying which was sent among them; and thus passed away the tenth year also; and the eleventh year also passed away in iniquity.
The social and religious divisions, which had quieted for a while, now begin to rise again.
Chronology: The eleventh year from the sign of the birth would be approximately A.D. 7.