In this addition to the scholarship on Mexican Americans, Neil Foley follows standards and conventions traditionally used to interpret Hispanic/Latino history. He acknowledges, as have others before him, that the history of Mexican Americans has its beginnings in the Spanish conquest of the Americas, and of Mexico in particular. He concurs with other historians that there exist certain watershed eras in that history: these include the War with Mexico (1846–1848); the Mexican Revolution of 1910; the Depression era; World War II; the decade of the Chicano movement; and the rise to prominence of the Hispanic Generation. As have those who preceded him, Foley adopts a chronological schema to guide the narrative.

But Foley is not recycling an old chronicle. He adds to and surpasses the competing literature by undertaking an incredible amount of research in heretofore untapped archives and other sparsely used collections. His contribution to the role of Mexican nationals in the making of America, for instance, relies on the Archivo General de la Nación, the Archivo Histórico de la Secretaría de Relaciones Exteriores (AHSRE), and the archived papers of some of Mexico's presidents. His sources for the Mexican-American role in the making of America include the public records of Texas governors, the papers of civil rights leaders such as George I. Sánchez and Hector P. García, and documents found in the US National Archives.

The value of Foley's sources becomes evident early on, in his elaboration of early twentieth-century immigration and naturalization topics. The case of Timoteo Andrade (1929) is by now well known to scholars, but Foley expands on the episode by utilizing the AHSRE and setting the case against the backdrop of other court decisions on whiteness and citizenship. Though Andrade ultimately was allowed naturalization, the affair left Mexicans wondering why white society negated them the opportunity and privilege of becoming Americans.

Foley's sources allow him to improve upon our knowledge of the ongoing diplomatic relationship between the United States and Mexico, as he ably shows how the two countries coordinated the Good Neighbor Policy during World War II. Foley further counts on new sources to document the contributions Mexican nationals (and Mexican Americans) made to World War II, calculating that approximately 14,943 Mexican nationals entered the armed forces. Mexico urged individuals who remained citizens of Mexico to perform military service and then worked closely with US officials to resolve problems—among them issues of qualifications, eligibility, deferments, exemptions, and ill treatment—afflicting her people in uniform. Not many other historians have addressed Mexico's assistance to and participation in the war effort. Mexico also helped in World War II by mobilizing an agricultural work force in the form of braceros. Foley augments old works by culling the columns of Spanish-language newspapers such as Excelsior and Acción and researching consular reports, the Manuel Ávila Camacho papers, US State Department documents, and other archival materials. Using many of the same sources, he adds to existing knowledge on Operation Wetback of the 1950s.

Foley's chapter on the history of Chicanos (in his view, the term describes the children of the immigrants) provides fresh insight on the period, due in part to his use of Texas governors’ archives. The treatment of post-1970s immigration is further enlightening. Foley notes that by the end of the twentieth century, major changes had taken place: mainstream America had acknowledged the immigrants’ presence, immigrants were acculturating easily into the American way of life, and nativists’ worries that immigrants would destroy the nation had not come to pass. However, efforts to curtail immigration through legislation persisted.

Foley is an award-winning historian and Mexicans in the Making of Americas can only enhance his already well-established reputation. Reminiscent of Elliott Robert Barkan's All Points West (2007), Foley's opus is another reminder that many contributing to the making of America were of foreign birth.