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 [no. 80].
The document further denounced the arms race as “an utterly treacherous trap for humanity, and one which injures the poor to an intolerable degree” [no. 81].
These teachings grounded the U.S. Bishops’ 1983 peace pastoral, with its special focus on nuclear weapons. Applying just-war criteria, the bishops declared the use of such weapons against civilian populations to be immoral [no. 147], first-strike use to be morally unjustifiable [no. 150], and “limited” use to be morally “highly skeptical” [no. 159]. They taught “strictly conditioned moral acceptance” of nuclear deterrence policy, only justifiable as a step toward disarmament [no. 173]. The arms race was “an act of aggression against the poor” [no. 128]; and they urged reduced armaments, bans on chemical and biological weapons, and cuts in conventional forces.
In the decades following, having witnessed the People Power Revolution of 1983-86 in the Philippines and peaceful revolutions ending communism in Eastern Europe in 1989, the worldwide Church seemed to be moving towards a stronger endorsement of pacifism. Contemporary war is so destructive that during the past thirty years it has seemed less and less defensible—as Catholic leaders argued in opposing the U.S./United Kingdom invasion of Iraq in 2003 and as Saint Pope John Paul II contended in opposing both the 1990 Gulf War and the Iraq war.
In addition, while nuclear war fears seem less acute now than during the “nuclear freeze movement” in the 1980s, concerns continue about the proliferation of nuclear weapons. Witness the current consternation over Iran’s possible acquisition of such weapons, North Korea’s testing of ballistic missiles, the nuclear weapons of India and Pakistan, and recent calls for the U.S. to engage in a nuclear build-up. Against this background, it is highly encouraging that Pope Francis has renewed the Catholic Church’s opposition to nuclear proliferation, leading the Vatican to spearhead global support for the Treaty on the Prohibition of Nuclear Weapons, which recently went into effect with the requisite number of signatory nations. Church advocacy for banning nuclear weapons emphasizes both the security concerns associated with these dangerous weapons of mass destruction as well as devastation that the arms race brings to the world’s poor by diverting human, scientific, and financial resources from development needs to war.
In addition, just war principles challenge contemporary war-making on two fronts: what the tradition called jus ad bellum (justice in going to war) and jus in bello (justice in waging war). Under contemporary circumstances, it seems less and less likely that the deployment of weapons can measure up to either set of potential criteria for justifying the use of force. Weighty moral concerns attach to all forms of aggression today: “civil wars” as in Syria; the arms trade, both conventional and nuclear; resort to violent revolution by aggrieved minorities; terrorism and the responses to terrorists embedded with civilian populations; and use of “drones” and other more “automated” weapons that can seem to make war “easier.” The task of justifying any of these appears more and more illusory with each passing year.
Following the Council’s lead, recent popes (especially Saint Pope John Paul II, Pope Benedict XVI and Pope Francis) have been in the forefront of global calls for strengthening the United Nations, improvements in international protection of refugees, and the ability of international entities to intervene in violent disputes even within a single country. The urgency of peacemaking has never been more apparent than it is today.
 National Conference of Catholic Bishops. The Challenge of Peace: God’s Promise and Our Response, May 3, 1983.
 “The World’s Most Dangerous Border” and “A Rivalry That Threatens the World” in The Economist, May 21-27, 2011.