Mormon 4:2

And it came to pass that the armies of the Nephites were driven back again to the land of Desolation. And while they were yet weary, a fresh army of the Lamanites did come upon them; and they had a sore battle, insomuch that the Lamanites did take possession of the city Desolation, and did slay many of the Nephites, and did take many prisoners;

The Nephite armies were pushed back to the land of Desolation. While they were still tired, a new Lamanite army came and attacked them. They had a hard battle. The Lamanites took over the city Desolation. They killed many Nephites and took many prisoners.

The Nephite armies were driven back to Desolation. While they were still exhausted, a fresh Lamanite army hit them hard. The battle was brutal. The Lamanites took the city of Desolation, killed many Nephites, and captured even more.