On Sunday the overwhelmingly Catholic island of Guam prayed for peace amid a military standoff that threatens its very existence.

North Korea had threatened to attack the US territory, prompting President Donald Trump to warn the regime of Kim Jong-un to expect “fire and fury like the world has never seen”.

North Korea’s threat is serious: it has been testing intercontinental ballistic missiles with the ability to reach the US mainland. According to some reports it has also successfully miniaturised a nuclear warhead to mount on those missiles.

Since the fall of the Soviet Union, the issue of nuclear war has largely disappeared from the public consciousness, but is now once again a major concern ­ which gives a new relevance to the Church’s teaching on nuclear weapons, their use and deployment, and the history of intra-Catholic debate on the subject.

Vatican II document Gaudium et Spes is clear in condemning all acts of war that indiscriminately kill civilians, as nuclear war does. “Any act of war aimed indiscriminately at the destruction of entire cities or of extensive areas along with their population is a crime against God and man himself. It merits unequivocal and unhesitating condemnation,” the document says.

But this raises questions: could nuclear weapons ever be justified if they were used against purely military targets? And is it permissible to maintain them as a deterrent?

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