U. S. - Mexican War: Part IV


U.S. Campaigns in the Mexican War

The United States had a small regular army, but could quickly swell its ranks with volunteers, and had a cadre of professional military officers trained at the United States Military Academy (known as West Point). West Point graduates who served as lieutenants in the Mexican War would command armies on both sides in the War Between the States. Their names are instantly recognizable to students of the American Civil War: George G. Meade, Ulysses S. Grant, George B. McClellan, P.G.T. Beauregard, Braxton Bragg, Joseph E. Johnston, and Robert E. Lee.

The U.S-Mexican came at the close of the Napoleonic Era of warfare, where battles were fought primarily between lines of musketeers trained to fire in volleys, supplemented by cavalry and cannon. By the 1860's, during the American Civil War, this kind of warfare generated enormous casaulties, with the introduction of rifles and canister and Gatling guns which could mow down an entire formation in seconds. Throughout the entire war, the United States suffered 13,000 casualties and the Mexicans perhaps in excess of 20,000. By contrast, in a single Civil War engagement (Gettysburg in 1863, between Mexican War veterans Lee and Meade) the Confederates lost 28,000 and the Union 23,000.

In the U.S. Mexican-War, both sides were armed predominantly with muzzle-loaded smooth bore muskets with a relatively short range (compared with rifles) and a nasty kick. The Mexicans had inferior British-surplus flintlocks, and tended to fire them from the hip to avoid taking the recoil on the shoulder. U.S. Dragoons (light cavalry) and Texas Rangers had new Colt revolvers, which, while a handgun, could fire five or six shots without reloading.

Some regiments of U.S. artillery had horses, not just to pull the cannons and ammunition, but for the men who fired them. The mounted cannoneers, or "flying artillery" as they were called, could be deployed much faster than typical artillery personnel of the period, who had to walk or ride on the guns. This allowed the arillery to be placed right on the battlefield (instead of hiding far behind the lines)and used on infantry before they could march close enough to use their muskets. Zachary Taylor used the tactic several times with very favorable results. During the Civil War, the tactic was tried but had to be abandoned. Facing rifles, which had a considerably longer range than muskets, artillery deployed on the field would be cut to pieces.

Zachary Taylor’s Pre-war Texas Campaign

In July 1845, the Texans accepted the invitation to join the United States and President Polk ordered General Zachary Taylor,later to be twelfth President of the United States, to organize U.S. forces in the area of Corpus Christi, Texas. Taylor had picked up the nickname “Old Rough and Ready” from his days of fighting wars against the Seminoles in Florida.

In January, 1846, Polk ordered Taylor to advance to the Rio Grande and also ordered Commodore David Conner to set up a blockcade of the Mexican port of Vera Cruz.

General Taylor's Fort Texas was, from the Mexican point of view, in Mexico, and a blockade was, of course, an act of war. While Texas was a province of New Spain, its southern boundary had been the Nueces River, which flows into the Gulf of Mexico at Corpus Christi. The United States had recognized this boundary in its 1819 treaty with Spain (which ceded Florida to the U.S.). The Texans, however, claimed their new Republic extended to the Rio Grande (or Rio Brazos, as the Mexicans call it).

While the United States Constitution makes the President commander of the armed forces, only Congress has the power to declare war. See U.S.Const., Article I, Section 8. Nonetheless, without a declaration of war, in March 1846, General Taylor advanced to the mouth of the Rio Grande and established Fort Texas (later Fort Brown, the site of Brownsville, Texas) opposite Matamoros.

On April 25, about 1,600 Mexican soldiers under General Arista crossed the Rio Grande, surrounded an American detachment and killed or captured its members.

On May 11, 1846, President Polk described the incident to Congress and declared that “Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil.” The dubiousness of this statement was well-known to opponents of war in Congress. Illinois’ freshman representative proposed House resolutions, requesting the President inform the House, “whether the spot of soil on which the blood of our citizens was shed, as in his message declared, was, or was not, within the territories of Spain, at least from the treaty of 1819 until the Mexican revolution?”. The resolutions, which go on to mention “the spot of soil” several more times, became known as the “Spot Resolutions”.

The congressman, whose name was Abraham Lincoln, when it came his turn to exercise Presidential power without a congressional declaration of war, did so in a manner quire similar to President Polk. Polk’s conduct set a precedent for U.S. Presidents to take belligerent actions unilaterally, and when war results, ask Congress to ratify the provocative behavior by "declaring" war. For example, Polk ordered the U.S. Navy to blockade Mexican ports, and Lincoln ordered the Navy the blockade the ports of the Confederate States, each before Congress could declare war. A century later, three successive U.S. Presidents would carry on a war in Vietnam for ten years without bothering to obtain Congress' approval.

On May 8 at Palo Alto, northeast of Fort Texas, the Mexicans and Americans exchanged artillery fire. This demonstrated that the U.S. Army had superior cannons. The next day, Arista fell back to more defensible terrain. The fight on May 9 at Resaca de la Palma that afternoon was especially bloody, but eventually Arista's poorly trained and ill-equipped army crumbled. The Mexicans retreated hastily across the Rio Grande. Fort Texas was safe and the Mexicans had suffered three times as many casualties as the Americans.

On May 13, 1846, Congress declared war on Mexico.

Kearny Conquers New Mexico

The upper Rio Grande valley of New Mexico was the most successful Spanish colony in all of Northern Mexico. The population of New Mexico dwarfed that of the missions in Texas and California:

“In 1821, when Mexico became independent of Spain, California was sparsely populated with something like 3,200 Mexicans. New Mexico, on the other hand, had a population of about 40,000 and was the dynamo of the northern frontier. Texas was also sparsely populated with about 2,500 Mexicans.” (Weber)

The New Mexico settlements were, however, isolated from Mexico proper by distance and hostile natives. The “Santa Fe Trail”, the overland route to St. Louis, was a much shorter, safer and easier trade route than the Camino Real down through El Paso. The central government also gave the Spanish and civilized Pueblo people of New Mexico virtually no assistance in their constant warfare with the savage Apache and Navajo nations.

After the United States declared war on Mexico, General Stephen Watts Kearny and his Army of the West marched along the Santa Fe Trail into New Mexico’s undefended northern frontier. Governor Manuel Armijo declared his intention to confront the American army, but, in a series of secret meetings with representatives of the American government, Armijo was persuaded not to resist Kearny’s forces and instead fled south to El Paso. General Kearny entered Santa Fe on August 18, 1846, and took possession of New Mexico without firing a shot. In Santa Fe, Kearny was joined by famous scout Kit Carson, who would guide the dragoons over the Rockies to California. The Army's passage through the area now known as Arizona was likewise uncontested.

Battle of San Pasqual

Kearny’s forces did eventually encounter resistance. In the San Pasqual Valley southeast of Escondido, California, in the darkness of early morning on December 6, 1846, hungry, wet, and cold, the First Dragoons and Missouri Volunteers under Kearny, a force of around 120 men, encountered a force of Californios led by General Andres Pico. Pico, whose troops were outnumbered by the Americans, pretended to retreat. As the Americans pursued, the Californios wheeled around and charged with their lances. The tactic so surprised Kearny's troops that, following heavy casualties and running out of ammunition, they were forced to take up a defensive position atop a nearby mountain. Two Americans, Kit Carson and Edward Beale, escaped through the enemy lines to get reinforcements. Relief arrived from San Diego the following day. Reinforced by marines led by Commodore Robert Stockton, the Americans went on to win the Battle of San Gabriel on January 8 and January 9, 1847.

Battle of Monterrey

By September, 1846, Taylor had assembled 6,641 troops and launched his attack on Monterrey, in Northern Mexico. Logistics were difficult and progress was extremely slow. Gen. Pedro de Ampudia's army of 7,303 held many advantages behind fortified hills. Fighting was house-to-house. After three days of fighting, Ampudia offered to surrender the city if Taylor would permit withdrawal of the Mexican troops. Taylor accepted. Back east, the Battle of Monterrey was considered a third Taylor success, but Taylor had barely penetrated Mexico and his overland supply lines were already streched to the limit. President Polk transferred most of the seasoned soldiers to Gen. Winfield Scott for an amphibious landing at Vera Cruz and a strike at the heart of Mexico.

Before the Vera Cruz landing could be accomplished, General Santa Anna launched a counteroffensive against Taylor's forces, resulting in the Battle of Buena Vista in February 1847. Outnumbered by Santa Anna four to one, Taylor’s men hunkered down amid crags and gullies near Saltillo and fought off waves of Mexicans. After two days of struggle, Santa Anna retreated.

« U.S.-Mexican War, Part III: Mormon Battalion | U.S.-Mexican War, Part V: Halls of Montezuma »


David J. Weber, "The Borderlands on the Eve of War", http://www.pbs.org/kera/usmexicanwar/dialogues/usmexicanwar/borderlands/d8ceng.html.

The Handbook of Texas Online: http://www.tsha.utexas.edu/handbook/online/articles/view/TT/fta29.html


U.S. Army, American Military History, Chap. 8, “The Mexican War and After”, http://www.army.mil/cmh-pg/books/amh/AMH-08.htm

President Polk’s May 11, 1846, Special Message, Asking Congress to Declare War With Mexico: http://sunsite.unam.mx/revistas/1847/Polk-i.html

Lincoln’s response: the “Spot Resolutions” (facsimiles of the originals): http://www.archives.gov/digital_classroom/lessons/lincoln_spot_resolutions/lincoln_spot_resolutions.html

Mexican site on the war: The Mexican American War Memorial Home Page: http://sunsite.unam.mx/revistas/1847/Summa.html.

Historical context by team of Mexican writers: http://sunsite.unam.mx/revistas/1847/Exordium.html

Notes to Define the Sentence «Mexican-American War of 1846-1848.», by Gabino Sánchez. Gabino Sánchez (tr. Verónica Rojas); http://sunsite.unam.mx/revistas/1847/notes.html;

Mexican Map: http://sunsite.unam.mx/revistas/1847/Mapa_1.jpg.