In April 1846, tensions between the U.S. and Mexico along the disputed border were high. About half of the U.S. Army, then tiny, was camped outside of Matamoros, Mexico, and rumors were flying that the much larger and better outfitted Mexican army was about to undertake efforts to remove the troops from their territory. Captain Seth Brett Thornton led his 2nd mounted dragoons on an expedition to try to confirm those rumors and gain intelligence about the military’s plans. He rode his command—which included about thirty percent of the Army’s mounted troops—straight into an ambush and lost his entire command. His ill-luck both exposed the position of the Mexican army and escalated the events that would become known as the Mexican-American War.