03/01/2012 03:33 pm ET Updated May 01, 2012

Foreign Policy's Amen Corner

Review of Sword of the Spirit, Shield of Faith: Religion in American War and Diplomacy. By Andrew Preston. Alfred A. Knopf. 832 pp. $37.50

Soon after Sept. 11, 2001, a Lutheran minister told George W. Bush "you are a servant of God called for such a time like this." The president replied: "I accept the responsibility." Convinced that he was "here for a reason" and would be judged for his actions, Bush declared his intention to launch a "crusade" against Islamic terrorists, invoked Judeo-Christian traditions of religious tolerance to deter Americans from seeking revenge against all Muslims, and drew on the language of faith to bless the nation's wars in Afghanistan and Iraq.

Some critics charged that Bush's rhetoric was a radical break with diplomatic history, breaching the wall separating religion and politics. According to Andrew Preston, however, his words "rested comfortably" with practices, reaching back four centuries, which used religion to frame foreign policy objectives. In Sword of the Spirit, Shield of Faith, Preston, who teaches American history at Cambridge University, provides an astute, judicious and sweeping survey of the themes that have animated this often-ignored relationship, documenting the links between religion, democracy, and individual liberty; America's manifest destiny; the justification of force in an unjust world; the existence of evil as a test to the faithful; and the obligations -- and temptations -- that accompany wealth and power.

Preston demonstrates, often to a fare-thee-well, that virtually all of America's presidents have religious "mindsets." William McKinley's claim that he asked for (and received) divine guidance before deciding to go to war with Spain was not, he argues, window dressing to obscure his economic and political motives. Like his fellow, mainline Protestants, Woodrow Wilson advocated war as a last resort, a means to ensure a righteous world perpetually at peace.

Less well known is the religiosity of Franklin Roosevelt and Dwight Eisenhower. FDR, Preston suggests, was the first president "to prioritize faith itself, as opposed to Protestantism or even Christianity, as the essence of American democracy," insisting that without it there could be no morality. Although his faith was theologically vague and he could be irreverent ("Oh goddammit, we forgot the silent prayer," he exclaimed at a Cabinet meeting) Eisenhower, the first president to be baptized while in office, believed that religion distinguished a just America from a materialistic, atheistic Soviet Union, "which knew no god but force."

A religious perspective, Preston notes, also informed critiques of American foreign policy. Dissenters believed, in the words of journalist E.J. Dionne, that "faith is more credible when it stands as a challenge, when it insists on aspirations beyond those of our own political movements, communities or nations." Denouncing America's occupation of the Philippines, William Jennings Bryan, a Christian fundamentalist, declared that the Bible's command to "'preach the gospel to every creature' has no Gatling gun attachment." A.J. Muste, a Congregationalist minister, was a leading World War I era pacifist (and later an adviser to Martin Luther King). And, of course, two Catholic priests, Dan and Philip Berrigan, poured vials of their own blood on files in a Baltimore Selective Service office to bear witness to their opposition to the war in Vietnam.

Clearly, religion has provided a shared language for leaders and the public throughout American history. Preston believes it is a "missing link, a vital but unrecognized part of the story," which has sometimes "constituted a critically important factor."

It's difficult, however, to measure whether religion has had a "powerfully enduring influence on the conduct of American war and diplomacy." Preston acknowledges, for example, that John Foster Dulles's assertion that "were it not for the churches of this country there probably would not be a United Nations today" was a stretch. But he insists, with a vagueness that renders refutation almost impossible, that the claim is "not entirely without justification."

"It is impossible to know, definitely," Preston admits, whether religious opposition to the Vietnam War had an impact on policy. "Most likely," he concludes, it did not limit Lyndon Johnson's options (including escalation), "at least not directly" -- only to add that there are "tantalizing hints" that Secretary of Defense Robert McNamara was so troubled by the critique of religious dissenters that he posed "the most serious internal challenge to Johnson's war strategy."

Perhaps. But McNamara's attendance at a Presbyterian Sunday School when he was a youngster, his awareness of the philosophical and ethical dimensions of Christian thought and of "the moral intensity of the anti-war movement" do not make a compelling case for a religious basis for McNamara's turnaround.

People, it is said, have two reasons for their actions: a good reason and the real reason. Even they don't always know which is which. And so, it may be sufficient to show, as Preston does, that in America, "where free politics and free religion thrive together in tandem," appeals to the sword of the spirit and the shield of faith, for better and worse, resonate -- and motivate.