Despite ample evidence that foreign policy and religion commingle in American minds and have done so throughout U.S. history, historians too often divorce these fields from one other. Issues of war and peace are fraught with religious underpinnings that naturally affect how people address those issues, but historic ignorance of this factor undermines the ability of scholars to grasp American diplomacy completely. Recent trends toward filling this historiographical lacuna benefit understandings of various eras by demonstrating the role of religion in the response of American leaders and citizens to international affairs. In another step toward fixing this problem, Markku Ruotsila offers an insightful examination into the influence of Christian institutions and leaders on the U.S. debate over entry into the League of Nations after World War I. He focuses on conservative evangelical opposition to U.S. participation and then traces this legacy to the present.

Ruotsila outlines the significant role Christianity played in American perceptions of the League of Nations and international affairs immediately after World War I. The book begins with a broad overview of the Social Gospel and how Progressive religious leaders championed the League as not only an international body for administering diplomacy but also as part of a religious force propelling the world toward a more tranquil existence. The author demonstrates that the Social Gospel movement had a pivotal sway on the establishment of the League of Nations. Ruotsila then details how, why, and when confessional Christians in the United States campaigned against the League. This conservative Christian effort ultimately contributed to the reasons that Congress failed to ratify U.S. entry. In other words, conservative Christian leaders opposed the League of Nations on religious grounds, convinced constituents and politicians of their position, and thereby became a key factor in defeating the U.S. attempt to join it.

Ruotsila delineates Dispensational, Calvinist, Lutheran, Methodist, and Episcopalian opposition to American entry into the League of Nations, in each case providing solid documentation for how these entities theologically came to oppose the international body. Dispensationalists denounced the League as fulfilling the prophecy of a final world empire and as a sign of “human pretensions of self-sufficiency” in thinking that they could prevent the sin of war without God's help. Although many Calvinists backed the Social Gospel and therefore the League, conservatives, including Baptists, Presbyterians, and Christian Reformed, counter-argued that such a human endeavor to improve the world without a Christian core doomed it to failure. Furthermore, they lamented the lack of mission language in the League charter and warned against cooperating with non-Christian states on an equal plane. Lutherans argued against such Social Gospel endeavors because of their amillennialist bent and insistence on the separation of church and state. Conservative Methodists and Episcopalians found themselves in the minority within denominations that publicly endorsed the League of Nations but nonetheless derided it as dangerously socialist and too divorced from Christianity for success.

Ruotsila dedicates the last part of this well-researched and adeptly argued book to articulating how the Senate discourse against the League of Nations contained religiously charged language, even when the speaker did not intentionally want to fight U.S. participation on theological grounds. The author critiques groups that organized to oppose the League and their Christian connections and traces an anti-League of Nations Christian platform through the twentieth century, establishing a link to later conservative American Christian commentary on foreign affairs. Throughout this volume Ruotsila provides concise summaries of key ideologies and theologies, alongside brief biographical vignettes, especially when rooting the various entities and people and their anti-League sentiment to their diverse theological convictions. He also carefully explains what his sources can and cannot reveal, never overstating his case. A politician may have failed to make an overt religious connection to his opposition to the League, but his language nonetheless played into the Christian arguments against America's League entry.

One wonders just how much influence conservative Christian leaders and politicians had over popular sentiment about U.S. entry into the League of Nations because few lay voices appear in this study. While Ruotsila unearths a tremendous amount of writing and debate, it seldom leads to lay opinions or even popular reaction in general. It would help to know whether the constituents in a particular denomination agreed with their leaders. How widespread was the Methodist and Episcopalian opposition to their denomination? Did people read the writings of key theologians before taking a stance on the League of Nations? Ruotsila uses Lutheranism as a key example but dangerously lumps the numerous Lutheran denominations and factions together at times. While he outlines the various denominations and their myriad of ethnic and theological backgrounds, he too often reverts to speaking of the Lutheran Church—Missouri Synod as representative of Lutheranism. He would have been better served to isolate strictly the LCMS to avoid the muddy waters of Lutheran infighting and factionalism.

These points should not detract from a very good volume. Ruotsila demonstrates yet again why scholars of religion and diplomatic historians should study together more often. In the key debate over U.S. entry into the League of Nations, won eventually by the naysayers, Ruotsila clearly shows the influence of conservative Christianity.