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 twenty miles west along the Rio Grande from Zachary Taylor's camp along the Rio Grande.:48 The much larger Mexican force completely 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.[1]:48