ontrary to peace. Therefore war is always a sin.

Obj. 4: Further, the exercise of a lawful thing is itself lawful, as
is evident in scientific exercises. But warlike exercises which take
place in tournaments are forbidden by the Church, since those who are
slain in these trials are deprived of ecclesiastical burial.
Therefore it seems that war is a sin in itself.

_On the contrary,_ Augustine says in a sermon on the son of the
centurion [*Ep. ad Marcel. cxxxviii]: "If the Christian Religion
forbade war altogether, those who sought salutary advice in the
Gospel would rather have been counselled to cast aside their arms,
and to give up soldiering altogether. _On the contrary,_ they were
told: 'Do violence to no man . . . and be content with your pay'
[*Luke 3:14]. If he commanded them to be content with their pay, he
did not forbid soldiering."

_I answer that,_ In order for a war to be just, three things are
necessary. First, the authority of the sovereign by whose command the
war is to be waged. For it is not the business of a private
individual to declare war, because he can seek for redress of his
rights from the tribunal of his superior. Moreover it is not the
business of a private individual to summon together the people, which
has to be done in wartime. And as the care of the common weal is
committed to those who are in authority, it is their business to
watch over the common weal of the city, kingdom or province subject
to them. And just as it is lawful for them to have recourse to the
sword in defending that common weal against internal disturbances,
when they punish evil-doers, according to the words of the Apostle
(Rom. 13:4): "He beareth not the sword in vain: for he is God's
minister, an avenger to execute wrath upon him that doth evil"; so
too, it is their business to have recourse to the sword of war in
defending the common weal against external enemies. Hence it is said
to those who are in authority (Ps. 81:4): "Rescue the poor: and
deliver the needy out of the hand of the sinner"; and for this reason
Augustine says (Contra Faust. xxii, 75): "The natural order conducive
to peace among mortals demands that the power to declare and counsel
war should be in the hands of those who hold the supreme authority."

Secondly, a just cause is required, namely that those who are
attacked, should be attacked because they deserve it on account of
some fault. Wherefore Augustine says (QQ. in Hept., qu. x, super
Jos