In portraying the development of [the traditional Christian just war] doctrine, I rely a great deal upon two preeminent theologians in history, Thomas Aquinas from the thirteenth century and John Calvin from the sixteenth.
Why these two?
First (and most simply), Aquinas and Calvin are untainted by modern liberalism's distorted views of both religion and war and thus provide a useful Christian antidote to these distortions. Second (and more complicated), Aquinas and Calvin offer an approach to war that motivates Christians to be shaped morally and spiritually so they can act well on the battlefield and also in everyday life, which is something missing in almost every other modern perspective on war.
Aquinas and Calvin present an account of just war that is grounded in the character of God ...~ Dr. Darrell Cole, When God Says War Is Right, p. 2