Question: If the object of war is to kill people and destroy property, how can there ever be such a thing as a "just war"? How can anyone square such actions with the Ten Commandments?
Answer:. War is never just if it is fought for the purposes of killing or destruction. Nor is war just if it is fought for the conquest or subjugation of other people. Much like the defense of one's self and family, or the public prosecution of criminals, a just war is one fought by a nation to defend itself against present or future aggression. That is to say that all just wars are defensive.
The Ten Commandments are a brief summary of the moral law, found in the Old Testament books of Exodus and Deuteronomy (chapters 20 and 5, respectively). Read in their biblical context, it is clear that they don't proscribe killing in self defense, just war, or enforcement of the moral law against capital crimes. Indeed the Hebrew is properly translated, "Thou shalt not murder," an injunction only against unjust killing.
A number of conditions must be met for a war to be just:
It should be obvious that there is tremendous potential for abuse in the waging of modern war. There has not been a perfectly just government since the Old Testament repudiation of God's rule in favor of King Saul. But citizens must do their best to ensure that their rulers conduct war according to Christian principles.
Question: Saint Thomas says nothing of
non-combatants in his answer on just war. Who made up this requirement?
St. Thomas Aquinas did not mention this requirement in the Summa because in his time it was taken for granted in Christian civilization. War was conducted by soldiers against soldiers. It was fairly well regulated by a code of honor that kept soldiers from preying on the innocent, and even from attacking combatants by surprise or if unarmed. Civilians still got killed occasionally, and property still got damaged, but at least the destruction was normally not directly intended. Unfortunately, things have gone down hill since Saint Thomas -- an understatement among understatements!
At the time of the American Revolution this concept of soldiers fighting soldiers remained largely intact. There was some indignation about Indian style ambushes, but war remained largely a military concern.
In Western civilization the first use of military troops against a civilian population was that of General Sherman in his US Civil War "March to the Sea," under the authority of Abraham Lincoln. The Lincoln era saw a shift from federal government in the Americas, and small kingdoms and duchies in Europe to the liberal, and often highly aggressive, nation state. (Blessed Pope Pius IX, feeling the same pressures in Europe, sympathized with the Confederacy.) But even after Lincoln -- and in most other engagements of the Civil War -- the idea of just war being restricted to combatants was still a strong principle in Western moral belief and practice.
Industrialization brought with it the idea that the enemy's productive capacity to make war was a legitimate target for military action. One might bomb the enemy's ball-bearing factories, or his shipyards, or his railroads, among other possible examples. Civilians might get killed accidentally, but at least the direct intention was the elimination of war-making capacity. The dividing line between combatant and non-combatant began to get more blurry, but the distinction was recognized by Western countries, and was made in practice.
In the years between world wars, the US was a signatory to a treaty requiring the evacuation of civilians from cargo ships before those ships could be destroyed by a submarine, and even that was considered by at least one American admiral (Thomas C. Hart) as drawing too close "to the inhumane features of German submarine warfare." When General "Billy" Mitchell began to promote the idea of an "Air Force" in the 1920s he was careful to picture it as a defensive arm, as the idea of bombing populated centers was too obviously immoral. One of the ways Roosevelt took to popularize American entry into WW-II was to publicize the barbaric nature of the Japanese who had killed 2000 civilians in air attacks on twenty Chinese cities. Even at the end of the war, General LeMay was dropping leaflets warning civilians to evacuate areas planned to be bombed -- and the possibility was at least discussed of inviting Japanese officials to witness a demonstration of the A-bomb instead of dropping it on a city without warning.
It is not possible to paint a completely favorable or unfavorable picture of Allied or Axis tactics in WW-II. The bombing of Hamburg, the bombing of Britain with V-1s, and the bombing of Dresden all demonstrate that people can become callous and indiscriminate in war. (And, perhaps, a lesson about terroristic retaliation as well.)
One might be tempted to blame technology. Big bombs are difficult to target against the munitions factory while avoiding the neighboring residential areas. But, here again, we have seen civilized nations making the effort. The Norden bombsight was a moderately successful WW-II attempt to do just that, as were the "smart bombs" of the Gulf War.
War is a terrible thing -- not at all as it is glorified in movies and novels -- to be avoided if at all possible. War is a consequence of sin; of the fallen nature of man caused by original sin, particularly among the un-baptized; of the actual sins that we ourselves commit, and allow to be committed in our society; of being ignorant of God in the Blessed Trinity, and of the fact that He became one of us, to redeem all of us, and to offer us the power of becoming adopted sons and daughters of God. The remedy for war should be obvious.
With regard to the September 11th attacks, Islam has been an expansionist, war-like religion, making converts by the sword, ever since Mohammed got his start by raiding camel caravans. Those who fail to consider this historical reality will make it more difficult to ensure the future safety of what used to be "Christendom." Nonetheless, that does not make law abiding Muslims complicit in the attack. The proper response of the United States to terrorist attacks is to identify and punish the guilty. Not doing so will invite more attacks. But shooting at an unknown enemy or "carpet-bombing" a civilian population may well allow the guilty to go free, turn us into the guilty party, and provoke another group to further terrorist attacks as their only means of retaliation. Turning Afghanistan "into a sea of glass," may sound great in a saloon with a beer in one's hand -- it is not the appropriate reaction of even nominally Christian people.