The Thornton Affair (also called the Thornton Skirmish) was an incident between the militaries of the United States and Mexico that served as the primary motivator that caused U.S. President James K. Polk to ask for a declaration of war against Mexico in 1846, sparking the Mexican-American War.

The incident is clouded by over a century and a half of propaganda, half truths, and great exaggerations by the participants on both sides. However, it can be ascertained that the event occurred sometime around dusk on April 25, 1846, and continued in the early hours of April 26.

A company of seventy U.S. Dragoons commanded by Capt. Seth Thornton was ordered to scout an area about twenty miles (30 km) northwest of what later became Brownsville, Texas. On the 25th, the Dragoons, acting on the advice of a local guide, investigated an abandoned hacienda. What precisely happened after this point is not entirely clear; however, some two thousand Mexican soldiers under the command of Col. Anastasio Torrejón were encamped in and around the hacienda, and a firefight occurred. Both sides fought ferociously, but the greatly outnumbered U.S. force was forced to surrender after several hours of skirmishing.

During the skirmish, some sixteen U.S. troopers were killed, with an unknown number of Mexican dead. Thornton and many of his officers were taken prisoner, and held in Matamoros, Tamaulipas, as prisoners of war. Upon learning of the incident, President Polk asked for a declaration of war before a joint session of the United States Congress, summing up the need for war by famously stating:

"American blood has been shed on American soil".

On May 13, 1846, Congress declared war on Mexico, despite protestations by the Mexican government that Thornton had crossed the border into Mexican Texas — a border that Mexico claimed began south of the Nueces River, and which the United States claimed began further to the south at the Rio Grande (Río Bravo). The ensuing Mexican-American War was waged from 1846-1848, and witnessed the loss of many thousands of lives and nearly two thirds of the territory of Mexico.

See also

• Battles of the Mexican-American War
• Mexican-American War

References

Bauer, K. Jack "The Mexican-American War 1846-48"