Open border
At the end of the Mexican-American War (1846–48), the Treaty of Guadalupe Hidalgo, by which the United States took about 50 percent of Mexican territory, established the current international border between the United States and Mexico. Throughout the nineteenth century, the border was essentially open to the movement of people and goods. The diagrams on the left show the gradual changes, as buildings were being set back farther and farther from the international line.