 On war, Thomas is an exponent of a version of the “just war” theory Augustine took from the ancient Romans. For a war to be just, it must be commanded by someone in authority, there must be a just cause, and it must be carried on without disproportionate violence. It is not justifiable to lie to an enemy, since that would destroy the trust that will be needed to restore peace  (see Summa, 2–2, q. 40, a. 1, a. 3).