Alma 52:13

and thus he was endeavoring to harrass the Nephites, and to draw away a part of their forces to that part of the land, while he had commanded those which he had left to possess the cities which he had taken, that they should also harrass the Nephites on the borders by the East Sea; and should take possession of their lands as much as it were in their power, according to the power of their armies.

He was trying to attack the Nephites. He wanted to pull some of their armies to that part of the land. At the same time, he told the men he left behind to keep the cities he had taken. They should also attack the Nephites along the coast by the East Sea. They should take as much land as they could with their armies.

His strategy was to harass the Nephites and draw part of their forces to that side of the land, while the troops he’d left behind to hold the captured cities would keep attacking the Nephites along the eastern coast—seizing as much land as they could with whatever strength they had.