Donald Trump’s decision to send National Guard troops to the U.S.-Mexican border is only the latest in a long history of U.S. militarization of its national boundaries.  

In fact, America’s southern border—which has shifted multiple times with U.S. expansion—was arguably formed through violence. Texas and American militias used force to establish that border in the 1830s and 1840s, capturing modern-day states like California, Texas, and all of the American southwest from Mexico.

In the decades after, the both official and vigilante groups violently regulated the movement of people across that border—be they Native Americans, escaped slaves, Chinese immigrants, or Mexicans.