Hostilities between U.S. and Mexican troops commenced on 25 April 1846 with Mexican troops killing and capturing a number of U.S. Army dragoons in the future state of Texas. The Battle of Palo Alto, the first major battle of the Mexican–American War, was fought on 8 May 1846, a few miles from the modern-day city of Brownsville, Texas. A force of some 3,400 Mexican troops (a portion of the "Army of The North") led by Mexican General Mariano Arista engaged a force of 2,400 United States troops under General Zachary Taylor. Taylor's forces drove the Mexicans from the field. The United States Congress responded to these hostilities by issuing a declaration of war against Mexico on 13 May 1846 – the Mexican–American War had begun.