Alma 59:7

and thus being exceeding numerous, yea, and receiving strength from day to day, by the command of Ammoron, they came forth against the people of Nephihah, and they did begin to slay them with an exceeding great slaughter.

The Lamanite army was very big. It kept getting bigger every day. Ammoron told them to attack the people of Nephihah. They started killing many of them.

The enemy forces grew enormous, gaining strength daily. Under Ammoron’s orders, they attacked Nephihah and began slaughtering the people there.