On April 25, 1846, a 2,000-strong Mexican cavalry detachment attacked a 70-man U.S. patrol that had been sent into the contested territory north of the Rio Grande and south of the Nueces River. The Mexican cavalry routed the patrol, killing 16 U.S. soldiers in what later became known as the Thornton Affair. Both nations declared war. In the ensuing Mexican–American War, there were no more battles fought in Texas, but it became a major staging point for the American invasion of northern Mexico.