[64][65] Learning of the Thornton Affair, Polk told Congress in May that a war between Mexico and the U.S. had begun.[66][67]
That same month, Taylor commanded American forces at the Battle of Palo Alto and the nearby Battle of Resaca de la Palma. Though greatly outnumbered, he defeated the Mexican "Army of the North" commanded by General Mariano Arista, and forced the troops back across the Rio Grande.[68][69] Taylor was later praised for his humane treatment of the wounded Mexican soldiers before the prisoner exchange with Arista, giving them the same care as was given to American wounded. After tending to the wounded, he performed the last rites for the dead of both the American and Mexican soldiers killed during the battle.[70]
These victories made him a popular hero, and in May 1846 Taylor received a brevet promotion to major general and a formal commendation from Congress.[71] In June, he was promoted to the full rank of major general.[72] The national press compared him to George Washington and Andrew Jackson, both generals who had ascended to the presidency, but Taylor denied any interest in running for office. 