Alma 54:9

This chapter includes epistles between Moroni and Ammoron.  As I read both epistles I noticed a huge difference between the two.  Moroni was concerned about preserving his people and getting his prisoners back so that they could be protected again. Ammoron was more concerned about revenge and righting the wrongs he felt against him. Moroni tells Ammoron:

"And now behold, we are prepared to receive you; yea, and except you withdraw your purposes, behold, ye will pull down the wrath of that God whom ye have rejected upon you, even to your utter destruction."

Moroni and his men had God on their side and fought in His name. They knew their cause was just and that the Lamanites were not just. Moroni knew that he could defeat the Lamanites with the help of the Lord, but he gave them chances to be saved. Moroni shows mercy.