Boundary between the United States and Mexico, map by William H.
Emory, 1855 Between 1849 and 1857, the Army Corps of
Topographical Engineers marked and mapped the U.S.-Mexico
boundary and published a report on natural features of the
borderland. The vast new western territories immediately became
a focus of congressional dispute regarding slavery in new
states. This map shows the border between New Mexico and
Chihuahua, Mexico. Geography and Map Division, Library of
Congress