The first major conflict of the Mexican War occurs north of the Rio Grande River at Palo Alto, Texas when United States troops under the command of Major General Zachary Taylor rout a larger Mexican force. Zachary had been ordered by President Polk to seize disputed Texas land settled by Mexicans. War is declared by the United States against Mexico on May 13, backed by southerners while northern Whigs were in opposition. Ten days later, Mexico declares war back.