Moroni “was exceedingly wroth because of the stubbornness of those people whom he had labored with so much diligence to preserve.” That was the very point of his title of liberty, and the point of all of the work he had done to fortify the defenses of the cities that were part of the land of Zarahemla.
His response was dramatic, but accompanied by the voice of the people, he received permission to force those who would not take up arms to join the army. Those who were to be compelled were those who had refused to fight for this invasion, and did not include the Ammonites, who declined to fight because of a previous oath.