Risking Immeasurable Harm makes an important contribution to the historiography by delineating the role that diplomatic pressure from the Mexican government played in limiting U.S. anti-immigrant measures in the pivotal period from 1924 to 1932. This period included the end of the so-called “Roaring Twenties” as well as the Great Depression. As historian Mai Ngai has argued, the 1920s featured attempts on a global scale to centralize the power of the nation-state—and specifically the notion of state sovereignty—by means of immigration restrictions. In 1926, B. Traven, a foreign-born resident of Mexico whose origins remain subject to debate, drove this point home in a possibly autobiographical novel, The Death Ship, which features a decrepit boat sailing the sea with a cargo of undocumented workers in search of a country to accept these migrants.Indeed, immigration restrictions were as powerful a political issue in the late 1920s and early 1930s as they are now. For Mexico, emigration to the United States served as an important escape valve at a time when three major rebellions—de la Huerta (1923–1924), Cristero (1926–1929), and Escobar (1929)—pitted citizens against a central government only gradually strengthening after the ravages of the first decade of the Mexican Revolution (1910–1920). At the same time, Mexican exiles threatened the stability of that government by plotting revolts, as Julian Dodson and others have demonstrated in recent scholarship. A well-regulated immigration policy hence benefited both governments.However, deep racial resentments precluded rational immigration policies. A State Department official considered Mexicans “backward, intellectually infantile, illiterate, prone to violence, inherently undemocratic” (p. 27). Advocates of legal restrictions believed Mexicans to be “a hazard to U.S. society and its institutions” (p. 126). Nonetheless, initial U.S. restrictions against immigrants from Mexico were “administrative” rather than “legislative” restrictions. In other words, restrictions were the result of a nascent immigration enforcement apparatus (much of which shared such ideas) rather than the product of legislation, and adherents of a quota did not get their wish, even after the onset of the Great Depression. In 1930, when a U.S. senator from Georgia, William J. Harris, proposed a bill instituting the first-ever quota system on Mexican immigration; administrative restrictions were so effective that “not a single common laborer…gained legal admittance into the United States for over a year” (p. 234). Thus, the Harris Bill failed precisely because administrative restrictions had been so effective. Not only had Mexicans been kept out, but the Great Depression had also eliminated the jobs that had attracted them in the first place. In addition, the U.S. government also removed U.S. citizens of Mexican descent from the national territory.One strength of the book is its binational lens on a topic that has usually been examined chiefly through an exclusively U.S. perspective. Montoya brings the Mexican perspective to life by drawing upon Mexican archival sources. However, these sources make fewer appearances in the notes than their U.S. counterparts. The author omits one important archive—the Fideicomiso Archivos Plutarco Elías Calles y Fernando Torreblanca, which houses the papers of several Mexican presidents and policymakers of the 1920s and 1930s and is particularly valuable for the study of foreign relations. Montoya only uses English-language scholarship, thus eliding the perspective of important Mexican scholars such as Lorenzo Meyer and many others. Therefore, Risking Immeasurable Harm is valuable as a study of U.S. immigration policy and the input in it provided by agents of the Mexican state and by the Mexican immigrants themselves. Montoya summarizes this input on p. 250 in explaining why the U.S. government opted for administrative restrictions over legislative strictures when it came to immigration from Mexico: “administrative restriction was the perfect compromise between a Westphalian sense of national sovereignty and a Wilsonian notion of more cooperative diplomatic relations.” From the Mexican perspective, the reality of how many Mexicans crossed the border was not as important as the absence of a formal discriminatory quota system and limits to a racialized discourse that discriminated against Mexicans.Taking an expansive view of immigration policies and practices beyond immigration law, this book is a valuable contribution to specialists interested in the history of immigration into the United States. It shows the complexity of the internal debates in the United States over immigration policy, as well as the role in Mexican diplomats and agents in these debates.