In speaking about who authorizes war St. Thomas emphasizes that the sovereign has the responsibility for the common good of those committed to his care. Only he can declare war. Moreover the sovereign has the lawful right of recourse to "the sword" to defend his people against internal strife by punishing those who do evil, justified by St. Paul in verse 4 of chapter 13 in the letter to the Romans. Therefore it is his duty to defend the common good against external enemies by having recourse to arms. A just cause is required to wage war. St. Thomas considers such a cause to be "that those who are attacked, should be attacked because they deserve it on account of some fault."6 Although St. Augustine introduced the idea of a just war and the middle Ages furthered its cause, it was not until the 16th and 17th centuries that a complete theory, which included the proper waging of a war, was established. Two names of importance regarding this development are Vitoria and Suarez. Fr. Conway, S.J., has synthesized their teaching. Hostilities are divided into two classes: an armed attack against a peaceful society and injurious actions taken against the same (generally defined as an infringement of a right). The first class from which an armed response resulted would be considered as a defensive war. This type of war was distinguished from the second-class hostility. An armed response to an injurious action was considered an offensive or aggressive war. According to Vitoria and Suarez a defensive war needed "no special moral justification."7. They saw an armed response as an involuntary act forced upon a nation. On the other hand, the aggressive war needed to be justified. An injurious action done does not involve destruction and death so how was it possible for the Christian willfully to choose war as a response? The problem for them arose from the conflict between a Christian wanting love and peace but responding with death and destruction.
