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U.S. President Barack Obama, left, and his Russian counterpart Dmitry Medvedev, right, shake hands at a press conference after signing the newly completed "New START" treaty reducing long-range nuclear weapons at the Prague Castle in Prague, Czech Republic Thursday, April 8, 2010.

When President Barack Obama and Russian President Dmitry Medvedev met in Prague to sign a new agreement on nuclear weapons, it marked one more step in the religious community's long campaign to reduce, if not end, the threat of nuclear war.

The Strategic Arms Reduction Treaty, or START, aims to reduce each country's deployed strategic warheads to about 1,550 each, and cut the number of launchers from the currently permitted 1,600 to 800. It also would cap nuclear-armed missiles and bombers.

For Christian denominations both at home and abroad, it represents a major victory in a campaign that has waxed and waned since the first atomic bombs were dropped at the end of World War II.

U.S. President Barack Obama, left, shake hands with his Russian counterpart Dmitry Medvedev, right, after signing the newly completed "New START"
U.S. President Barack Obama, left, shake hands with his Russian counterpart Dmitry Medvedev, right, after signing the newly completed "New START" treaty reducing long-range nuclear weapons at the Prague Castle in Prague, Czech Republic Thursday, April 8, 2010. (AP Photo/Petr David Josek)

On Aug. 20, 1945, just days after the bombings of Hiroshima and Nagasaki, Protestant leaders issued a statement expressing their "unmitigated condemnation" of the attacks.

Less than a year later, a commission that included theologians Reinhold Niebuhr and John C. Bennett issued a report that declared, "We have sinned grievously against the laws of God" in using nuclear weapons.

But as David Cortright, director of policy studies at the Kroc Institute for International Peace Studies at the University of Notre Dame, has noted, an ambivalence marked Christians' responses to the bomb over time.

"As the Cold War intensified in the late 1940s, some of those who had greeted the bomb with horror now came to accept it as a necessary deterrent against godless communism and the perceived threat of totalitarian aggression," he wrote in the Spring 2009 issue of Yale Divinity School's journal Reflections.

The 1980s saw a resurgence of religious and secular anti-nuclear campaigns, including the Catholic bishops' 1983 pastoral letter, "The Challenge of Peace," and organizing by the evangelical social justice group Sojourners. The National Association of Evangelicals joined the push later in the 1980s.

More recently, the so-called "new evangelicals" have organized the Two Futures Project, a movement that calls for the abolition of all nuclear weapons.

The Catholic bishops' 1983 letter put the nation's largest religious community squarely in the midst of the public debate over the Reagan administration's nuclear arms policies. The bishops endorsed a "no-first-use" declaration by the United States and voiced support for a comprehensive test ban treaty, both of which continue to be sticky issues in arms-control debates.

The bishops, though, supported continuing the policy of deterrence even while making their approval "strictly conditional" and "a step on the way to progressive disarmament."

U.S. Protestant denominations and international bodies such as the World Council of Churches, however, pushed beyond the Catholic bishops to hold up an abolitionist vision of a world without nuclear weapons.

In 1986, United Methodist bishops published their own pastoral statement, "In Defense of Creation," which forthrightly rejected deterrence and said the doctrine "must no longer receive the church's blessing." Presbyterians also have a long history of opposition to the nuclear arms race, stretching back to 1946.

On the international level, both the WCC and the Vatican, under a succession of popes, have been outspoken opponents of the arms race and any use of nuclear weapons. Pope John Paul II edged the Catholic Church close to pacifism, declaring there are next to no conditions in a nuclear age that justify nations going to war with one another.

It is a vision the churches keep before them.

"The moral end is clear: a world free of the threat of nuclear weapons," Archbishop Edwin O'Brien of Baltimore told the Global Zero Summit in February.