The subject of Rachel St. John's book, Line in the Sand, published by Princeton University Press in 2011, is revealed in the subtitle: "A History of the Western U.S.-Mexico Border." St. John focuses her attention on the desert to the West of the Rio Grande, beginning with the notional creation of the border following the Mexican-American War in 1848. The major theme of the book is the way in which the border developed from being "a mere line on a map" in the middle of the nineteenth century, to becoming a heavily guarded frontier, the subject of a huge amount of regulation and legislation. At the same time as the border itself changed, so did life on either side of it. In 1848, when the border was easy to cross, people on both sides of the line lived fairly similar lives. This became less true over the decades, and with the difference came more rigorous enforcement of the divide.

St. John includes the stories of many individuals affected by the border, particularly those who attempted to challenge it, such as Henry Alexander Crabb who, in 1857, attempted to establish an independent republic in Sonora. She relates the ways in which ranchers, miners, immigrants, smugglers, and many other groups responded to the gradual creation of a hard border between two countries which were developing in quite different directions.

The "line in the sand" being referred to here is the western US-Mexico border. This informative book covers the entire history of this border, starting with its creation back at the end of the Mexican-American War in 1848. It explains how, over the years, this border has been transformed from a line on the map to a heavily guarded boundary between the two countries.

St. John goes into elaborate detail about how various parties, such as American railroad workers and miners and Mexican immigrants, have been impacted by this border. At one stage, the US decreed that no Chinese nationals could enter the country. Authorities at this border crossing enforced this law, so it has not only been Mexican immigrants affected over the years.

The book also discusses the factors which worked together in the early days to make the US-Mexico border a flexible barrier that prevented certain people, goods, and animals from crossing the border and allowed others to pass without hindrance. St. John masterfully tells the tale of both the Wild West days and the more modern era of fences and immigration authorities.

With topics such as border control and immigration reform being a fundamental element of US politics in 2020 and beyond, this book provides a comprehensive and highly useful history of this border.