Alma Ch44

With the Lamanites being surrounded, they are given a choice to surrender or be destroyed, and they are stubborn enough to reject the offer and keep fighting. Of course they are defeated because of their lack of preparing for the battle against the Nephites.
Zerahemnah was the commander of the Lamanite army so Moroni begins to talk to him as he is standing in the river with his army, surrounded by Nephites (v1). Moroni explains that he doesn't want this war and the Lord has been the one to strengthen them because they have faith that they will be preserved as long as they are faithful (v2-4). Captain Moroni demands from Zerahemnah, in the name of God, to deliver up the weapons of war and promise not to ever come again to attack the Nephites or be cut down where they stand (v5-7).
Knowing that they will lose if they continue to battle, Zerahemnah says we don't believe it was God who delivered us, you all are just tricky so we will surrender now and plan to come back later (v8-9). Moroni refused their surrender because they wouldn't promise to not come back and Zerahemnah got mad and tried to surprise attack but was scalped by one of Captain Moroni's guards who declared to the Lamanite army that they could either continue to fight or depart with a covenant of peace (v10-14). Many of the lamanites were freaked out by the whole scalping things and departed with a covenant of peace while the remaining were angry and fought ferociously (v15-16).
I feel like "Moroni was angry" is close to saying he was annoyed because the Lamanites were stubborn and continued to fight until they were almost all slain at which point Zerahemnah suddenly says he will take Moroni's offer from before (v17-19). Moroni was merciful and stopped the bloodshed and took the weapons of the Lamanites and let them leave after they covenanted for peace (ha yeah...peace, its only the beginning), and so many had died from that battle that they didn't bother counting they just threw them all in the river to stay (v20-22). The army of the Nephites dispersed and went back to their families as the 18th year ends and also the record of Alma the younger (v23-24).