In Risking Immeasurable Harm, Benjamin Montoya examines the factors behind, and the response to, a campaign in the United States during the late 1920s and early 1930s to impose tough restrictions on Mexican immigration. Though measures enacted between 1917 and 1924 had significantly curtailed the flow of migrants to the United States from Europe and Asia, the national quotas introduced by this legislation did not apply to the countries of the Western Hemisphere. A concern over Mexican immigration in particular—fueled largely, as Montoya shows, by the view that Mexican migrants were racially inferior and unassimilable—prompted restrictionists to seek to remedy this omission. Calls by some legislators for an extension of the quota were opposed by the State Department, which argued that such a move would damage an improving relationship with Mexico's postrevolutionary government. In a bid to defuse congressional efforts to write new limits on Mexican immigration into law, consular officials resorted to “administrative restriction”—the much stricter application of existing rules and regulations—to bring about a substantial reduction in the legal cross-border movement of Mexican workers. With the successful application of this strategy, followed by a reversal in the flow of migrants with the massive repatriation of Mexicans during the early years of the Great Depression, the push for additional legal curbs on Mexican immigration dissipated, and a potential crisis in bilateral relations was averted.Montoya's study captures a moment at which immigration was at once becoming increasingly prominent as a domestic political issue and emerging as a phenomenon that could affect relationships between states. He provides a valuable account of the way in which the United States resisted acknowledging that immigration could be a legitimate foreign policy issue, insisting to other governments that bilateral or multilateral approaches to managing migration would impinge on US sovereignty to an unacceptable extent. Nonetheless, top officials such as Secretary of State Frank Kellogg were mindful of the potential consequences for US foreign relations of a less welcoming immigration regime for citizens of Mexico and other American nations. Indeed, Kellogg told a Senate committee in 1928 that the introduction of a quota would “adversely affect the present good relations” enjoyed by the United States across the Western Hemisphere and that it would be especially unfortunate to imperil an improved relationship with Mexico that was “a source of considerable satisfaction to [the US] government” (pp. 75–76).A central contention of Risking Immeasurable Harm is that it was largely “diplomatic pressure”—rather than economic considerations—that “prevented congressional efforts to curb Mexican immigration” (p. 1). There is little evidence, however, that Mexican diplomatic representations or activism by Mexican officials had a significant bearing on the course or outcome of the debate over immigration restriction. Though Foreign Minister Genaro Estrada is said to have warned US ambassador Dwight Morrow that the imposition of a quota would give rise to “considerable feeling” on the part of the Mexican people, Mexican leaders generally accepted the right of the US government to regulate immigration as it saw fit and were ambivalent about the phenomenon of migration to the United States in any case (p. 89). US officials recognized, however, that Mexican public opinion would deeply resent the insult of an immigration quota that was justified on the grounds of the supposed inferiority and undesirability of the Mexican people. (It is noteworthy that Montoya's citations of Mexican press comment on proposals for immigration restriction show that he encountered the relevant clippings in US diplomatic files, giving an indication of the way in which US officials monitored and assessed Mexican views on the issue.) Administrative restriction was therefore seen as a preferable way to assuage congressional concerns. Though the effect—a massive reduction in Mexican immigration—was the same, the rigid application of literacy, health, and passport requirements did not carry with it the same relationship-damaging sting of legislation founded on an assertion of racial superiority.Risking Immeasurable Harm draws on significant research in both US and Mexican archives to provide original analysis of an early and little-known episode in the history of immigration as an issue in the relationship between the two countries. (Perhaps unsurprisingly given the focus on a policy debate centered in Washington, there is a greater reliance on US sources than Mexican ones, and engagement with relevant secondary literature in Spanish is limited.) For historians of US foreign policy, this book also provides a fascinating early case study of an executive branch effort to avoid having constraints placed by Congress on its ability to conduct foreign relations.