In "Summa Theologica" Aquinas asserted that it is not always a sin to wage war and set out criteria for a just war. According to Aquinas, three requirements must be met: First, the war must be waged upon the command of a rightful sovereign. Second, the war needs to be waged for just cause, on account of some wrong the attacked have committed. Thirdly, warriors must have the right intent, namely to promote good and to avoid evil. Aquinas came to the conclusion that a just war could be offensive and that injustice should not be tolerated so as to avoid war. Nevertheless, Aquinas argued that violence must only be used as a last resort. On the battlefield, violence was only justified to the extent it was necessary. Soldiers needed to avoid cruelty and a just war was limited by the conduct of just combatants. Aquinas argued that it was only in the pursuit of justice, that the good intention of a moral act could justify negative consequences, including the killing of the innocent during a war.