The U.S.-Mexico border is a slippery subject. It is both a geographic reality and a malleable metaphor. It is crossed daily yet it is policed intensively. It is a powerful sovereign divide and also a unifying meeting point. In her book Line in the Sand: A History of the Western U.S.-Mexico Border, Rachel St. John does not shy away from the multiple meanings of the border. Instead, she demonstrates the specific ways that the border mattered, grounding her observations in rich and deep transnational research. This is a lively and elegant chronicle of the western land border's transformation from an idea in a treaty to a line on a map to a bustling commercial crossroads and, finally, to a heavily regulated zone of interaction. The contributions of the book are both historical and conceptual: St. John gives us new ways to think about the dynamics of borders generally while also painting a fascinating portrait of this border in particular. She artfully demonstrates that the border is not one thing but rather “a space of evolving and multiple meanings and forms” (3).

Chapters flow chronologically but can also stand alone thematically. Chapter 1 begins with surveyors' attempts to locate the border after its creation in the Treaty of Guadalupe Hidalgo in 1848. St. John's choice to focus on the western land border, spanning from El Paso to San Diego, is persuasive. The eastern border, running the length of Texas, had the Rio Grande as a natural divide. On the western border, in contrast, the U.S. and Mexico “conjured up an entirely new space where there had not been one before” (2). Lacking natural geographic dividing points, representatives from both governments had to negotiate a line through barren terrain, much of it uninhabited desert. Their efforts finally succeeded after years of travail, but the line on a map did not translate into instant territorial sovereignty. Chapter 2 chronicles the two primary challenges to the nascent border: Apache raiding and American filibustering. These activities violated the border, but, paradoxically, they also served to bolster it by galvanizing border residents to work together for border defense. In the 1880s, officials signed reciprocal crossing agreements, allowing troops to cross the border in pursuit of raiding Apaches.

Crossing agreements ushered in an era of binational cooperation, not just in border defense but also in commercial development. Chapter 3 chronicles the growth of industry and community in the 1880s and 1890s. In this era the border became not only a line demarking sovereign space but also “a place that people and corporations owned and called home” (63). For the most part, transnational capitalism was a unifying force, bringing together investors, laborers, and merchants in common cause. Commercial development led to state border policing. Chapter 4 describes the first concerted efforts to control the passage of goods and people across the border. Sovereignty was no longer measured in military might but instead in “customs collected, immigrants rejected, and bandits arrested” (90). This regime restricted cross-border movement, but only to a point: “sovereign principles,” St. John observes, “could be compromised with local needs” (117). Enforcement was characterized by a surprising amount of flexibility and binational cooperation. In Chapter 5, St. John shows the tragic ways that war—both the Mexican Revolution and World War I—interrupted and impaired this tenuous spirit of transnational collaboration.

Prohibition and other Progressive Era reforms led to the growth of vice districts on the Mexican side, drawing thrill-seeking Americans to cross the line. Chapter 6 chronicles the efforts of reformers to use the border as a tool to police morality, calling for border curfews and other methods to keep Americans from falling into sin. Chapter 7 delves into the use of the border to manage immigration. The ultimate challenge for the U.S. and Mexico was the creation of a “conditional border,” one that allowed for the entrance and passage of desired migrants and commerce but impeded the flow of those who were not welcome. Yet this was not a one-way proposition. The border was constituted, St. John writes, in a “process of complaint and accommodation by which government officials and private citizens negotiated sovereignty along the border” (175). This process continued even into the 1920s and 1930s, when immigration enforcement began its steady upward climb.

Line in the Sand proves that the border is as much a process as it is a line. It is made real not only by marks on a map but also by the specific actions and reactions of people living and working alongside. Its transgression by Apaches, soldiers, immigrants, smugglers and ordinary residents was strategic and conditional, testifying not to the border's weakness but rather to its power. This powerful and beautifully-crafted work should be required reading for all those interested in borders.