In over six hundred pages, Preston charts the scope and the centrality of religion in American politics, from the seventeenth century to the present. This book merges American history with the history of Christianity, and in doing so it qualifies the story of Christian empire. Unlike the Christian empires of the past, America has never had an established church. Nor did the American Revolution result in empire. The animating spirit behind much of Preston's narrative is Christian republicanism, and no Christian republic has ever had the territory or the influence or the power that the United States would come to possess.           

Preston's argument is worth outlining in detail. It has the shape of a double helix. One strand entails the melding of Christian sentiment with state power, through diplomatic maneuvers and the waging of war. This is the sword of the spirit, cherished by the Puritans and by George W. Bush alike. The other strand inverts the ideal of the church militant, appealing instead to a Christian hunger for international peace, for the beating of swords into ploughshares, for a fraternity of nations liberated from war. This is the shield of faith. Preston weaves these metaphors, both taken from Paul's letter to the Ephesians, into a sweeping historical analysis.

Seeking to explain why "U.S. foreign policy has often acquired the tenor of a moral crusade," Preston first turns his attention to the seventeenth century. Avidly Protestant, "the American colonies never underwent a counterreformation," he observes, and they waged almost continuous war against enemies deemed theologically other--i.e. Catholics and Native Americans. These Christian soldiers prided themselves on fighting holy wars, regularly fitting themselves into Old Testament patterns, the New World's Israelites imbued with "a consistent belief in America as a chosen nation and in Americans as a chosen people."            

Going forward, Preston accents the Protestant origins of the American Revolution. London was equated with Rome, and "the new political order [in America] newly codified a very old and very Protestant tradition of hostility to arbitrary power," Preston observes. American historians have outdone themselves in analyzing the Founders and the Enlightenment, the legacy of Hume and Montesquieu in American political thought. Preston notes that "Adams, Washington, and especially Jefferson cited Milton to justify or explain their political views," citations that reflect the rise of an American-style Christian republicanism. In the place of an established church, and opposed to the Church of England, not to mention the Church of Rome, was the first amendment to the constitution.

America's Christian republicanism could be warlike, and it could just as well be pacifist. A Vermont newspaper labeled the War of 1812 "a holy war," while this same war so outraged other (no less devout) New Englanders that they publically debated secession from the Union. The War of 1812 provoked "the first truly pacifistic antiwar movement" in the United States, Preston writes. Antiwar movements would continue to emanate from New England for centuries to come. In antebellum America, Christian republicanism nurtured the abolitionist spirit, and the Civil War was (among other things) a war over the proper relationship between the Christian faith and the American polity.

Preston applies a consciously contemporary vocabulary to the Civil War. This was "the nation's first war of humanitarian intervention," he states, with North and South construed as separate countries, one advanced and the other backwards. Abolitionists defined the Union's campaign as "a war of liberation." The Civil War marked another portentous development: the entry of Catholics into American civic life. What had been implacably Protestant, in the American self-conception, was becoming more broadly Christian and was destined to become Judeo-Christian in the twentieth century. Catholics, followed by Jews, did a great deal to link America to the outside world. So did millions of Protestant missionaries in the far-flung lands they were laboring to convert. In the second half of the nineteenth century, these American missionaries were "the brokers of global cultural exchange," Preston argues, just as the United States was inserting itself into the global economy and scrambling for empire with the great European powers.

Between World War I and World War II, pacifist aspirations kept colliding with the call for war. In fact, the American presidents of this period could only justify overseas war by promising international peace. Woodrow Wilson was the first to do so, motivated in his foreign policy by "Christian reformism," as Preston calls it. Wilson was drawn forward by his vision of a League of Nations, which was to be headquartered in Geneva, "the birthplace of Calvinism and the seat of Reformed Protestantism," Preston reminds us. Wilson's dreams collapsed beneath the opposition of more conservative American Protestants.

Where Woodrow Wilson failed, Franklin Roosevelt succeeded. FDR's was a "serene spirituality," and no less tenacious for its serenity. Synthesizing centuries of historical experience, FDR held "the Christian republican view that religion was the source of democratic freedom because it was the source of conscience and private belief," Preston writes. Roosevelt pushed this conviction in an ecumenical direction. Catholics and Jews were invited to participate in an American project sure to outshine the authoritarian evils of Nazi Germany and imperial Japan.

Preston moves from FDR to John Foster Dulles, who is often pictured as the archetypal anti-Soviet crusader, a dour Presbyterian who happily waved the sword of the spirit. Preston revises this caricature: an "ecumenical Christian," Dulles "stood at the crux of Protestant idealism and realism." In the 1940s, Dulles envisioned a world of postwar ploughshares, a joining of global hands, and was enraged when the Soviet Union refused to honor his vision. For Dulles, an idealistic dream of peace came to mandate an eventual Cold War realism.

Preston's double helix of an argument is visible throughout his Cold War chapters. He emphasizes the dissent of Christian liberals from Eisenhower's anti-communism, rightly dubbing the 1950s "an era falsely remembered for its homogeneity." The antiwar movement of the '60s widened such dissent. In reaction, the '70s witnessed an intensifying alliance between conservative Christians, together with a handful of rightward turning Jews, and the Republican Party.

The beneficiary of this reaction was Ronald Reagan, about whom Preston makes two shrewd points. One is that Reagan narrowed religion's political application, as opposed to Roosevelt and Truman, who sought something broadly national in their religious appeals, and as opposed to John Kennedy and Lyndon Johnson, who shied away from Judeo-Christian fervor. Reagan enthusiastically "deployed religious rhetoric to rally his supporters rather than to bind the nation together as a whole behind a common cause," Preston contends. And yet Reagan eschewed a holy war with the Soviet Union. His tactic was to imply an ecumenical, peace-loving bond between the American and Russian people, whatever the Politburo felt about the status of the Soviet soul. This is the climax of Preston's argument: "Reagan ... discarded the sword of the spirit for the shield of faith," and on these terms the Cold War came to its magical end.

Preston does not defer to the internet age, with its pressure to streamline, to simplify, and to bundle information behind a sensational thesis statement. Nor is this a conventional academic book: in fashioning an unapologetically master narrative, Preston juggles three centuries and multiple world religions. Coming after a generation of historians who discovered the minority in American history, Preston balances minority with majority in pursuit of his enormous question: in what way has religion invented America?