The Thornton Affair, also known as the Thornton Skirmish, Thornton's Defeat, or Rancho Carricitos was a battle in 1846 between the military forces of the United States and Mexico 20 miles (32 km) west upriver from Zachary Taylor's camp along the Rio Grande.: 48  The much larger Mexican force defeated the Americans in the opening of hostilities, and was the primary justification for U.S. President James K. Polk's call to Congress to declare war.: 48