Speaking to attendees of the Vatican’s November conference on “Perspectives for a World Free from Nuclear Weapons and for Integral Development,” Pope Francis “firmly condemned” even “the very possession” of nuclear weapons. In short, he judged not just nuclear war but also nuclear deterrence anathema. Supporters of his view hailed the pope’s statement as “historic” and a “big hit” to the efforts of nuclear powers such as the United States to stop the global momentum swelling behind last summer’s Treaty on the Prohibition of Nuclear Weapons. With 122 votes in support of the treaty in the United Nations, and the pope’s imprimatur, are we at last on the eve of the postnuclear millennium?...