The Mexican-American War on the Plains
By Randall Parrish in 1907
The year 1846 marked a pivotal moment in the relationship between the United States and Mexico. In April, Mexico formally declared war against the United States, a declaration swiftly followed by President James Polk’s call for 50,000 volunteers to take up arms. At the heart of the American strategy was General Stephen W. Kearny, a seasoned military leader entrusted with commanding the Western theater of operations. Kearny’s force was strategically divided into three distinct commands, each with a specific objective.
Kearny himself would lead the primary contingent westward toward the Pacific coast, aiming to secure control of crucial territories. A second force, consisting of a thousand volunteers under the command of Colonel Alexander W. Doniphan, was tasked with a daring southward advance into Chihuahua, a key Mexican state. The third division, under the leadership of Sterling Price, was assigned the critical responsibility of garrisoning Santa Fe, the capital of New Mexico, and maintaining American control over the newly acquired territory of New Mexico. The success of these operations hinged on the ability of the U.S. Army to project its power across the vast expanse of the Great Plains, a formidable challenge in itself.
In the historical record, Colonel Henry Inman preserved a remarkable anecdote tied to the unfolding events on the Plains, adding a layer of mystique to the Mexican-American War on the Plains.
"Early in the Spring of 1846, before it was known, or even conjectured, that a state of war would be declared, a caravan of 29 traders, on their way from Independence to Santa Fe, beheld, just after a storm, and a little before sunset, a perfect, distinct image of the Bird of Liberty, the American eagle, on the disc of the sun. When they saw it, they simultaneously and almost involuntarily exclaimed that in less than 12 months, the Eagle of Liberty would spread his broad plumes over the Plains of the West and that the flag of our country would wave over the cities of New Mexico and Chihuahua."
The weight and significance of this vision, and the accuracy of its prediction, remain open to individual interpretation and historical assessment. But for those involved, it added more fervor to the Mexican-American War on the Plains.
General Kearny’s army initiated its westward trek from Fort Leavenworth, Kansas, a crucial staging point for westward expansion. Throughout the summer of 1846, the army moved in separated columns, embarking on its arduous journey across the vast wilderness. The army consisted of two artillery batteries, three squadrons of the First U.S. Dragoons, the First Regiment of Missouri Cavalry, two infantry companies, and a contingent of Topographical Engineers. By August, these diverse elements had converged at a camp situated along the historic Santa Fe Trail, approximately nine miles downstream from Bent’s Fort, Colorado, strategically located on the banks of the Arkansas River. The details of this march, including the challenges and noteworthy events, were meticulously recorded by Lieutenant W.H. Emory, the commander of the Engineers, and John T. Hughes of the Missouri Cavalry, providing valuable insights into the realities of the Mexican-American War on the Plains.
The undertaking of marching a significant military force across such a considerable distance through an uninhabited region posed numerous logistical and strategic questions for officials. The absence of readily available supply depots and the severing of reinforcement possibilities raised concerns about the feasibility of the operation. It was considered an experiment, and a potentially perilous one at that. To mitigate the risk, the army transported vast quantities of provisions in heavily guarded wagons. Additionally, a substantial herd of beef cattle was driven alongside the troops, relying entirely on the nutritious buffalo grass that lined the trail for sustenance. At night, these cattle were typically confined within a corral formed by the wagons, although occasionally, they were tethered to iron picket pins driven deep into the hard ground. The journey was not without its initial challenges. Many of the horses, being only partially trained and unaccustomed to military displays, reacted nervously to the fluttering flags, the rumbling wagons, the blaring trumpets, and the clattering sabers. These factors led to numerous stampedes, as the frightened animals scattered wildly across the prairie, leaving riders and equipment behind. Despite the chaos, no serious injuries occurred, and the stray horses were eventually recovered. The details and challenges were what would be expected in the Mexican-American War on the Plains.
The troops moved in distinct formations. Records indicate that one such detachment established camp on July 9 in present-day McPherson County, Kansas, at the crossing of the Little Arkansas River. The abundance of mosquitoes, gnats, and black flies created a tormenting environment for both men and horses. Lieutenant-Colonel Ruff of the Missouri Volunteers commanded this particular group, and his men faced a severe shortage of provisions. Aware that a supply train was ahead, near Pawnee Fork, he dispatched a scout to intercept it and request a halt until his men could catch up.
As Ruff awaited the scout’s return, news reached him that Doniphan’s and Kearny’s men, trailing behind, were also struggling with dwindling supplies. To ensure timely relief, he sent additional messengers forward to locate the wagon train. Tragically, one of these couriers drowned while attempting to ford the Pawnee River. His body was recovered and given a military burial, marking the first casualty of the expedition on the Plains. John Hughes, the author of "Doniphan’s Expedition," vividly described the landscape that greeted the soldiers as they approached the Arkansas River. Comparing his account to the present-day appearance of the region highlights the profound changes brought about by settlement. This scene was part of the experience in the Mexican-American War on the Plains.
"In approaching the Arkansas River, a landscape of the most imposing and picturesque nature makes its appearance. While the green, glossy undulations of the prairie to the right seem to spread out in infinite successions, like waves subsiding after a storm, and covered with herds of gamboling buffalo, on the left, towering to a height of 75 to a 100 feet, rise the sun-gilt summits of the sandhills, along the base of which winds the broad, majestic river, bespeckled with verdant isles, thickly beset with cottonwood timber, the sandhills resembling heaps of driven snow."
On July 15, the separated detachments finally converged at Pawnee Fork, within the boundaries of modern-day Larned, Kansas. The river’s waters were too high to ford, prompting the soldiers to immediately fell cottonwood trees and construct a makeshift bridge. The army safely crossed the river on the tree trunks, carrying the sick and all camp equipment. The horses were forced to swim, while the empty wagons were floated across and hauled up the slippery bank by the soldiers. This process required two days of continuous labor. The small column then pressed onward, with the infantry marching alongside the cavalry. The soldiers’ feet became severely blistered, leaving a trail of blood in their wake. Two days later, somewhere along the Arkansas River, Major Howard, an officer previously sent to Santa Fe to gather intelligence, rejoined the main force. He reported that the common people of New Mexico were receptive to Kearny’s proposed peace terms, but the officials were hostile and actively preparing to resist the invasion. According to Howard, 2,300 men were already armed in Santa Fe, and another substantial force was rapidly being assembled in Taos. The American army greeted this news with enthusiastic cheers and renewed determination, eager for a confrontation. This energy was needed to proceed with the Mexican-American War on the Plains.
The Cimarron crossing of the Arkansas River was reached on July 20, marking a day of notable events. For the previous 30 miles, the column had been traversing areas teeming with vast herds of buffalo. Suddenly, a group of approximately 400 buffalo charged out of the valley and stampeded directly through the marching ranks. Chaos erupted, but the troops quickly regrouped and launched a counterattack, employing guns, pistols, and even drawn sabers, killing numerous animals and scattering the remainder across the Plains. During the advance up the river, a small number of Mexican prisoners were captured but later released. On July 29, the soldiers finally crossed the Arkansas River and established their first camp on Mexican territory, approximately eight miles downstream from Bent’s Fort. Here, they established strong guard lines to protect against both Mexican forces and Comanche Indians.
However, an unexpected threat emerged. During the night, prowling wolves triggered a stampede among the animals, causing over a thousand horses to break free from their restraints and dash wildly across the prairie, further agitated by the dangling lariats and pounding picket pins. Many of these horses were pursued for 30 to 50 miles before being recaptured, but nearly 100 were never recovered. During their stay at this camp, several Arapaho chiefs appeared and were treated with hospitality. They were particularly impressed by the army’s cannons. These were the dangers and challenges faced in the Mexican-American War on the Plains.
In preparation for a general advance, a 20-man scouting party, led by Lieutenant de Courcy, was dispatched to scout in the direction of Taos. During this mission, the party encountered an unusual problem involving the obstinacy of army mules, as recounted by the commander. He stated:
"We took three pack mules laden with provisions, and, as we did not expect to be long absent, the men took no extra clothing. Three days after we left the column, our mules fell, and neither gentle means nor the points of our sabers had the least effect on inducing them to rise. Their term of service with Uncle Sam was out. ‘What’s to be done?’ said the sergeant. ‘Dismount,’ said I. ‘Off with your shirts and drawers, men! Tie up the sleeves and legs, and each man bag one-twentieth part of the flour.’ Having done this, the bacon was also distributed to the men and tied to the cruppers of their saddles. Thus loaded, we pushed on without the slightest fear of our provision train being cut off."
On August 2, the American army, with flags waving and in full military formation, began its bold advance into enemy territory. As they passed Bent’s Fort, the occupants hoisted a large American flag, and the flat rooftops were filled with spectators, including many Mexican girls and Indian women. The troops continued their advance without incident until they approached the Mexican town of Las Vegas. Scouts then reported that the enemy was firmly entrenched in a mountain pass a few miles beyond the village, preparing to engage in battle. The soldiers immediately formed battle lines and advanced rapidly, with the dragoons and St. Louis Mounted Volunteers leading the way. Cartridges were distributed, the cannons were swabbed and readied, the port fires were ignited, and every rifle was loaded. The men were eager for combat. However, all these preparations proved unnecessary. Las Vegas was entered without a single shot fired, and the village officials swore an oath of allegiance to the United States, taking the oath upon the Cross instead of the Bible. The soldiers, eager for a fight, pressed on toward the canyon where they still hoped to confront the enemy. On August 16, near the village of San Jose on the Pecos River, three Mexican spies were captured. The most important of these, a son of General Salazar, was taken prisoner, while the others were released. It was later learned that these frightened Mexicans had reported to their people that the invading force numbered 5,000, supported by a vast number of cannons. The preparation was intense for the Mexican-American War on the Plains.
Manuel Armijo, the commander of the Mexican defenders, had assembled 7,000 troops, most of whom were well-armed, and occupied a strong position in Apache Canyon. However, the reports of the size of the invading force proved overwhelming for him and his men, despite his defiant letter to General Kearny the previous day offering battle. As the Americans reached the mouth of the canyon around noon, every man in the ranks was eager to test the resolve of the Mexicans. Lieutenant W. H. Emory described the scene:
"The sun shone with dazzling brightness; the guidons and colors of each squadron, regiment, and battalion were unfurled for the first time. The drooping horses seemed to take courage from the gay array. The trumpeters sounded ‘to horse’ with spirit, and the hills multiplied and reechoed the call. All wore the aspect of a gala day. About the middle of the day’s march, the two Pueblo Indians, previously sent to sound the chief men of that formidable tribe, were seen in the distance at full speed, with arms and legs both thumping the sides of their mules at every stride. Something was now surely in the wind. The smaller and foremost of the two dashed up to the general, his face radiant with joy, and exclaimed: ‘They are in the canyon, my brave; pluck up your courage and push them out.’"
However, the Mexicans were not there. The vaunted Mexican army had already disintegrated due to internal disputes and fear. The army had fled into the mountains, taking their commander with them. Another account added:
"As we approached the ancient town of Pecos, a large fat fellow, mounted on a mule, came toward us at full speed and, extending his hand to the general, congratulated him on the arrival of himself and his army. He said, with a roar of laughter, ‘Armijo and his troops have gone to hell, and the canyon is all clear.’"
Thus, New Mexico was easily won without bloodshed, and the centuries-long Spanish influence on the Great Plains was forever ended. The tides of war shifted south and west, beyond the boundaries of the region. With Doniphan’s hardships and struggles in the mountains and Kearny’s remarkable march across Arizona to California, there was little left to do in New Mexico. When Armijo abandoned the country, it became the undisputed possession of the United States, effectively concluding the conquest of New Mexico. The end of the Mexican-American War on the Plains changed the west forever.
Compiled and edited by Kathy Alexander, updated March 2025. About the Author: This article was written by Randall Parrish as a chapter of his book, The Great Plains: The Romance of Western American Exploration, Warfare, and Settlement, 1527-1870; published by A.C. McClurg & Co. in Chicago, 1907. Parrish also wrote several other books, including When Wilderness Was King, My Lady of the North, Historic Illinois, and others. The text as it appears here, however, is not verbatim, as it has been edited for clarity and ease for the modern reader.
Also See:
The Mexican-American War
Mexican-American War Timeline
Wars, Military, & Soldiers
Westward Expansion and Manifest Destiny