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During the Bush and Obama administrations, efforts to police the southern border of the United States increased dramatically. The size of the U.S. Border Patrol increased to 20,000 officers by 2013, making it the country's second-largest police force. Still, feeling that the federal government was not doing enough, groups of citizens in the Southwest took up arms and set up unofficial militias to patrol the border between Mexico and the United States. This tightened security over the border had an unintended consequence: not wanting to risk back-and-forth migration across the border, many immigrants opted to stay put after arriving to the United States.

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