On the evening of April 24, 1846, Captain Seth Thornton and 68 American dragoons “went to confirm intelligence that a Mexican military force had crossed the Rio Grande” just miles away from where Brigadier General Zachary Taylor was camped. Daniel Walker Howe, What Hath God Wrought: Transformation of America, 1815-1848, 731.
The following morning, the reports were proven to be true as a Mexican force attacked Captain Thornton and his soldiers at the Rancho de Carricitos. See id. The Mexicans killed 11 Americans and captured the remainder, with the exception of one wounded survivor, who was permitted to travel to Brigadier General Taylor and deliver the news of what happened. See id.
The Mexican-American War had begun. Zachary Taylor reported to Washington: “Hostilities may now be considered as commenced.” Id. at 732 citing Karl Jack Bauer, The Mexican War (New York, 1974), 48, 81.
Fourteen days later, Taylor’s message reached the White House. Daniel Walker Howe, What Hath God Wrought: Transformation of America, 1815-1848, 732. This did not come as a surprise to President James Polk and his cabinet, and in fact, they were already preparing a recommendation to Congress for a declaration of war against Mexico. Id. President Polk worked with his Secretary of State, James Buchanan, and his Secretary of the Navy, George Bancroft, in crafting his war message. Id.
When news spread of the outbreak of the war, some wondered why the American military was along the Rio Grande in the first place. See id. From the annexation of Texas, which was consummated just months earlier, the border with Mexico was an unresolved issue. See id. at 732-33. President Polk, however, wanted Texas to extend to the Rio Grande. Id. at 733. He sent General Zachary Taylor in 1845 into the Texan territory and as close to the Rio Grande as “prudence will dictate.” Id. at 734 quoting Orders of June 15 and July 30, 1845, quoted in David M. Pletcher, The Diplomacy of Annexation: Texas, Oregon, and the Mexican War, (Columbia, 1973), 255-56.
More than anything, President Polk wanted to expand America’s borders. That led some, like Texan President Anson Jones, to conclude that Polk wanted to “manufacture a war” between Texas and Mexico that America could intervene in and take over. Anson Jones, Memoranda and Official Correspondence (New York, 1859), 49.
Whether President Polk manufactured the war or simply put all the pieces in place to make war inevitable, his expansionist ambitions all but ensured that the war would break out. For the first time since the War of 1812, America was officially at war, and rather than defending itself, America was on the prowl for more land.