One of the natural but intellectually lazy responses of theologians in the 20th century was to react to the advent of nuclear weapons with the idea that just war theory was now somehow outdated or tired. There were some exceptions, like John Courtney Murray and Paul Ramsey, but the general tendency was to pay lip service to just war theory as having been maybe okay in times past, but to opt for a functional pacifism in a nuclear age. When this was done, it was pretended that the inadequacy or deficiency was in just war theory itself, and not in ourselves. To paraphrase and reapply Chesterton, it was not tried and found wanting, it was found difficult and not tried.
Just war theory says, among other things, that the violence of war can be justified if it is declared by a competent authority, if there is a formal declaration, if the cause is to rectify or prevent an injustice, if there is a reasonable chance of success, if it is waged with strict attention to proportion, and it is undertaken as a last resort. What could be wrong with this approach, except not following it?
Just war theory is a set of doctrines, and as such it cannot really get tired. Thinkers, however, can and do get tired.