It's been half a century since the US shrank by a square mile thanks to a combination of geography and politics. The Rio Grande, between Texas and Mexico, has shifted over the years—and its movements between El Paso, Texas, and Ciudad Juarez, Mexico have changed our borders. In 1864, it moved south thanks to heavy rains, and that added 700 acres of land to Texas. The area was dubbed the Chamizal, and it led to US-Mexico tensions.
A century later, Mexico maintained its link with Cuba amid the Cuban Missile Crisis, and the US grew worried about the country's potential fate in the Cold War. "Suddenly there's a real willingness to remedy the Chamizal dispute; to use it as a kind of bargaining chip," says a historian. Eventually, the US gave a portion of the area back to Mexico, NPR reports. Political implications aside, the move wasn't welcome to residents of the area, who numbered about 5,000. When her family was required to move, one recalls, "I remember my dad said, 'Don't look back. You are forbidden from looking back.'"