The line that defines
For nearly 2,000 miles, it runs alongside California, Arizona, New Mexico, and Texas. It begins in the east in Brownsville, Texas, and marches west along the Rio Grande, halting at the Pacific, in the town of Tijuana, notorious for its drug violence and reputation as a party spot for frat boys. Whatever the cause, the mythic U.S.-Mexico border draws millions of people to it each year. It’s the most frequently crossed international border in the world, and is one of the most intriguing unseen lines in history. Just ask Rachel St. John. In her new book, “Line in the Sand: A History of the Western U.S.-Mexico Border,” the Harvard associate professor of history traces the border’s origins to its modern-day consequences. The eastern U.S.-Mexico border was easy to establish: the Rio Grande forms a natural divide. But after the Treaty of Guadalupe Hidalgo ended the Mexican-American War in 1848, diplomats gathered with maps...