In the morning of August 6, 1945, a single bomb was dropped from an American airplane over the Japanese city of Hiroshima. When the bomb detonated, between 70,000 and 80,000 people were killed instantly, some of whom were completely incinerated by the intense heat. Many more died of the long-term effects of radiation sickness. Fires burned for three days, killing thousands of people who survived the explosion. Thousands more suffered from burns and radiation poisoning and had agonizing deaths. The final death toll has been estimated to be 140,000 by the end of 1945, the vast majority of whom were civilians. Many more died later from the long-term effects of radiation
Later that day, a statement by the President of the United States was released. In that statement, he said, "If they do not now accept our terms, they may expect a rain of ruin from the air, the like of which has never been seen on this earth."n
Three days later, on August 9, another bomb was dropped on the Japanese city of Nagasaki. Approximately 70,000 people were killed instantly. Because of the geography of the city, fires did not break out. But radiation poisoning did its worst, and in the end the death toll has been estimated at over 80,000 people, almost all of whom were civilians. Again, many thousands more died later from the long-term effects
The civilian casualties at Hiroshima and Nagasaki were not accidents or incidental. One of the specific intentions of the United States government in bombing cities and killing thousands of civilians was to terrorize the Japanese government into surrendering. If the Japanese had not surrended a week after Nagasaki, more atomic bombs would have been dropped over cities, causing tens of thousands more civilian deaths
The debate over the morality of the destruction of Hiroshima and Nagasaki has raged for decades. As an academic matter, the debate has some interest. But for Catholics, the issue has been definitively settled. In Gaudium et Spes, the Second Vatican Council said unequivocally:

The horror and perversity of war is immensely magnified by the addition of scientific weapons. For acts of war involving these weapons can inflict massive and indiscriminate destruction, thus going far beyond the bounds of legitimate defense…. All these considerations compel us to undertake an evaluation of war with an entirely new attitude. The men of our time must realize that they will have to give a somber reckoning of their deeds of war for the course of the future will depend greatly on the decisions they make today.

With these truths in mind, this most holy synod makes its own the condemnations of total war already pronounced by recent popes, and issues the following declaration.

Any act of war aimed indiscriminately at the destruction of entire cities or extensive areas along with their population is a crime against God and man himself. It merits unequivocal and unhesitating condemnation.

It is important to review these basic facts about atomic warfare and the clear and unequivocal teaching of the Church, because of the recent comments by the current President about North Korea. In terms appallingly similar to those of his predecessor, the President said,

North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen … They will be met with fire, fury and frankly power the likes of which this world has never seen before.

The President is not known for systematic and rigorous thinking on policy matters or for a throughtful approach to international relations. But this is not complicated — he has threatened to attack a nation with nuclear weapons, which would inevitably involve the wholesale destruction of cities and the horrible deaths of tens of thousands of people
In Gaudium et Spes, the Council Fathers warned:

The unique hazard of modern warfare consists in this: it provides those who possess modern scientific weapons with a kind of occasion for perpetrating just such abominations; moreover, through a certain inexorable chain of events, it can catapult men into the most atrocious decisions. That such may never truly happen in the future, the bishops of the whole world gathered together, beg all men, especially government officials and military leaders, to give unremitting thought to their gigantic responsibility before God and the entire human race.

The development of nuclear weapons by North Korea and their missile program are certainly destabilizing and undermine peace in the region. But threatening a nuclear attack on North Korea is dangerous and grossly irresponsible. Other means must be found to resolve even the most intractable of international disputes. The world has already seen the human cost of using nuclear weapons. We should pray that we never see it again.