First battle of Mexican-American war

Mexico won its independence from Spain, and soon after the Mexican State of Texas, already heavily populated by American settlers, began lobbying for its own independence — first with words, then with the capture of a Mexican army general, Antonio López de Santa Anna, who was first to acknowledge the sovereignty of Texas before his release. Still, Mexico rejected the general’s bargain, and claimed Texas for themselves even as the United States formally admitted the state into the union. Both sides massed troops at their respective borders; war was inevitable.

On this day, April 25, in 1846, a group of 70 U.S. dragoons led by Captain Seth Thornton were ordered to scout out an area near what today is Brownsville, Texas. They ran into a force of 2,000 Spanish soldiers, and after a fierce firefight that killed 16 of his squad, Thornton surrendered. That was the first skirmish of the Mexican-American war.

One member of the dragoons managed to escape back to camp, where he brought word of the Thornton Affair. That was all the justification President James K. Polk needed to declare war. Before a joint session of Congress he said “The cup of forbearance had been exhausted … Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil. She has proclaimed that hostilities have commenced, and that the two nations are now at war.”