Five generalizations can be made about the history of religion and foreign policy. First, notwithstanding the frequent, formulaic references to John Winthrop's "city upon a hill," the impact of Reformation era Protestantism is typically over-simplified and exaggerated. Appeals to an amorphous Providence and Enlightenment republicanism rather than invocations of a Puritan mission were the main motifs of nineteenth-century manifest destiny. Similarly, Presidents Thomas Jefferson and Theodore Roosevelt needed no Christian doctrine to bless their efforts to extend American power. Even those devout Protestants who tried to apply religious beliefs to foreign affairs not only disagreed about specifics, but also disputed the overall nature of the national mission. Although less often acknowledged than international Wilsonian activism, a visceral Bryanism—the sense that the United States should lead the world by separatist moral example—has been and remains a powerful force.
Second, religious beliefs and interests did not change the outcome of any first-rank foreign policy decision—for example, whether or not to declare independence, expand westward, develop an "informal empire" abroad, or fight a war. These factors, however, have affected the ways in which Americans framed and debated such major questions.
Third, religious concerns have influenced the outcome of some second-level foreign policy decisions. Abrogation of the Russian-American commercial treaty in 1912 and passage of the Jackson-Vanik Amendment in 1974 serve as cases in point. Awakenings and immigration have rendered "people of faith" increasingly diverse. In this pluralist context, religious interest groups have been most effective when they found allies outside of their own communities and invoked widely held American values.
Fourth, the role of missionaries merits special attention. As has been the case with businessmen and soldiers, a relatively small number of Americans were able to exert great influence—for good or ill—in a few distant lands. Missionaries not only facilitated political and economic expansion, either deliberately or inadvertently, but also inspired, educated, and infuriated foreign elites.
Fifth, major foreign policy decisions have affected domestic religious life more than the other way around. Often the effects were unanticipated. For instance, the revolutionary war with France undermined fears of "popery"; World War I exacerbated the multisided conflict among Catholics, Jews, Protestant modernists, and theological conservatives; and World War II sparked a religious revival that defied cosmopolitan predictions of secularization. These five general trends will probably persist for the foreseeable future, though with no diminution of ironic results.