I often troll for knowledge and provocation over at the social science research network (www.ssrn.com), and I usually find a fistful of both.
Most recently, I came across a piece written by David B. Kopel, titled "Evolving Christian Attitudes Towards Personal and National National Self-Defense." The full text is available for download here. The passage below is drawn from Kopel's abstract:
In the nineteenth and early in the twentieth centuries, the traditional Christian concepts of Just War and of the individual's duty to use force to defend himself and his family remained uncontroversial, as they had been for centuries. Disillusionment over World War One turned many Catholics and Protestants towards pacifism. Without necessarily adopting pacifism as a theory, they adopted pacifism as a practice. World War Two and the early Cold War ended the pacifist interlude for all but a few radical pacifists.
Beginning in the 1960s, much of the American Catholic leadership, like the leadership of mainline Protestant churches, turned sharply Left. Although churches did not repudiate their teachings on Just War, many Catholic and mainline Protestant leaders seemed unable to find any circumstances under which American or Western force actually was legitimate. Pacifism and anti-Americanism marched hand in hand. Today, pacifism now has greater respectability within orthodox Christianity than any time in the past 1700 years.