Updated January 2017
For most of U.S. history, little to no security existed along the southwest border with Mexico. This began to change after the United States enacted its first immigration quotas in the late 19th century. Irregular efforts to patrol the border began in 1904, and Congress officially established the Border Patrol in 1924. Early efforts focused mainly on unauthorized Chinese immigration and unlawful liquor smuggling.
Over the following decades, a focus on unauthorized immigration from Mexico led to substantial increases in the U.S. presence along the southern border. The total number of border agents has more than doubled since 2002, and the extent of border fencing has more than quadrupled since 2005. Investments in surveillance technology also increased substantially in the past decade, including a new network of mobile surveillance systems and watch towers. Today, the United States maintains an unprecedented level of investment in border security, particularly along the southwest border.