Rio Grande dispute between the United States and Mexico after the "Mexican War."
The Treaty of Guadalupe established the international border in the deepest part of the Rio Grande River, but the river kept changing its course and disputes over which country owned what land resulted. The disputed parcel of land between El Paso, Texas, and Ciudad Juarez, Chihuahua, was referred to as Chamizal.
With the resolution of the dispute in 1963,a National Park was established next to the Rio Grande River  and the international border in El Paso. Watch a video about this dispute, prepared by the National Park Service.