Perhaps the most important concept of the Mexican War that needs to be communicated to students today is simply that it occurred at all. The Mexican War has long been overshadowed by the American Civil War, which involved many of the same key figures and of course occurred on American soil, with devastating impact upon the entire populace. Even when students are aware that a war was fought between the United States and Mexico, it is often irrevocably linked with the Alamo and the Texas War of Independence, despite the separation of the two conflicts by a decade.

While I would not argue that it should receive equal coverage to the Civil War, the Mexican War is worthy of study in its own right. It represented many key military firsts for the United States, each with long-lasting ramifications. It was the first conflict fought entirely on enemy soil, the first war of open conquest, and it included the first occupation of a subjugated enemy. It was the first American war that included graduates of the United States Military Academy as a major component of the officers’ ranks, though they certainly did not hold the highest leadership positions. On a related noted, it was the first significant military action for many of the key leaders of the Civil War, who absorbed its lessons and sought to apply them in the later conflict, often with disastrous results.

For the modern student, or the instructor who likes to draw modern parallels with past events, there are many similarities between the Mexican War and the current war in Iraq. Both conflicts included an invasion of enemy territory, where American expeditionary forces faced a numerically superior enemy. In each war, the United States dispatched mixed forces consisting of regulars already serving in the army and wartime volunteers. In Mexico, militia forces played a substantial role, often in the same function as that performed by National Guard and Army Reserves in Iraq. American forces utilized superior technology in Mexico, in the form of better field artillery and units armed with rifles. Likewise, the 2003 invasion of Iraq involved the most technologically advanced military force ever fielded. Poor logistical planning, particularly for combat in a desert environment, plagued each invasion. Both wars included a campaign to capture the enemy capital, which remained under American occupation for a significant period of time. On each campaign, and during each occupation, American forces faced guerrilla units engaging in harassing attacks on supply convoys and isolated outposts. Each war lasted considerably longer than originally expected, due in part to the dissolution of the enemy government, which prevented any formal surrender to American forces. Finally, during the period leading up to each conflict, American leaders pursued diplomatic approaches to head off other potential conflicts that otherwise simultaneously occur. In the 1840s, this involved solving the question of ownership of the Oregon Territory before it could provoke the third war with Great Britain in less than a century. In the twenty-first century, this included overtures, some conciliatory, some threatening, to other potential belligerents, including Iran and North Korea.

The Mexican War offers a unique opportunity to present the divisions of American politics in the era preceding the Civil War. It offers many intriguing questions that demonstrate the growing sectionalism within the United   States, and offers an interesting way to present the continual dialogue over the expansion, retention, or abolition of slavery. Who proposed declaring war upon Mexico, and what did they hope to gain from the conflict? Who opposed the war, and on what grounds? How did the goals of the conflict change as the war stretched beyond a single campaign season? All of these concepts are complex, yet they are also answerable with careful study. Studying the Mexican War also an excellent way to examine the inherent problems associated with beginning a conflict without having clear national aims, and with radically altering strategy in the middle of a war. From a geopolitical standpoint, the ramifications of the war remain relevant today.

Any study of the Mexican War should begin with a clear understanding of the key concepts of the conflict, and unfortunately, in this regard, most American textbooks do a poor job of examining the events. Most textbooks characterize the Mexican War as a land grab by the United States, driven by greedy Southern slaveholders anxious to expand the territory available for chattel slavery. This oversimplified approach is surprising, given the vital relationship between the two nations in the modern world. It is also unfortunate, in that many of these works discuss the context of the war, but not the actual conflict. In truth, the Mexican War was the deadliest war in American history when measured by casualties as a percentage of combatants. Fully 20 percent of American soldiers who fought in Mexico died there, but only one-tenth of the casualties occurred on the battlefield, and thus this war is often treated as almost bloodless when compared to the Civil War’s tremendous cost in lives. The vast majority of American casualties in Mexico involved infectious diseases, many of them treatable or preventable. The horrendous mortality rate stimulated the development of military medical systems, and highlighted the need for discipline and proper hygiene within the military.

The Mexican War should also be considered in the light of the conflict that did not occur, namely, a war with Britain over possession of the Oregon Country. During the 1844 presidential contest, the Democratic Party platform called for territorial expansion to the Pacific Ocean, following the concept of “Manifest Destiny.” This platform also called for the immediate annexation of Texas, an action that had been rejected by the three preceding administrations. When James K. Polk became the first dark-horse candidate to win a presidential election, he dispatched emissaries to Mexico in the hope of purchasing the land between Texas and the Pacific Ocean, but such entreaties were firmly rebuffed by the Mexican government, which skeptically viewed American intentions toward Texas. In settling the Oregon dispute, the Polk administration never seriously considered provoking a war with Great Britain, despite the cries of some partisans that the United States should claim ownership beyond the 54^th parallel. The cry of “54º40´ or fight!” called for conquest of the entire disputed zone, but cooler heads prevailed, and the simple solution of extending the Treaty of 1818’s line at the 49^th parallel presented a fair compromise. If the diplomatic relationship with Great Britain was marked by logic and an equitable outcome, the Polk administration’s approach to Mexico was quite the opposite, appearing almost calculated to provoke a war.

Despite repeated warnings that Mexico still considered Texas a renegade province, and would regard any annexation of Texan territory tantamount to an act of war, the Polk administration quickly moved to not only admit Texas as a state, but to defend it against any potential Mexican aggression. Mexico and the Republic of Texas had never formally agreed to the border between their territories, with Mexico insisting that the border was at the Rio Nueces, near San Antonio, and Texas claiming land to the Rio Grande, near Corpus Christi. Naturally, Polk supported the Texan contention, and to back the newly-admitted American territory, he dispatched Major General Zachary Taylor and a small army to the north bank of the Rio Grande. At the same time, Mexican troops crossed the Rio Grande, intent upon defending their version of the border at the Nueces. Each side interpreted the other’s movement as an invasion of sovereign territory, and when the two forces blundered into one another, each could claim it had shed blood defending its own soil from an invader. For both sides of the war, therefore, it was at least nominally a defensive fight, provoked by the enemy.

American strategists at the beginning of the conflict made a fundamental mistake: assuming that the enemy would see the situation in the same way as American commanders. Specifically, Polk, Taylor, and General-in-Chief Winfield Scott all believed that a victory over Mexico should be fairly simple and would not require a significant investment of time, troops, or treasure. A blockade would strangle Mexican commerce and protect American shipping, while an invasion of Mexican territory south and west of Texas would demonstrate American resolve. Economic factors, coupled with the hopelessness of the military situation, would quickly compel Mexico to surrender to avoid further destruction. Of course, Mexico did not view the situation in the same way. Mexican commanders expected to fight a defensive struggle, using a professional army that outnumbered the American regulars by a factor of three to one. European observers agreed with the Mexicans, and believed the United   States stood little chance of prosecuting a war on Mexican soil.

While the Mexican Army outnumbered the U.S. Regulars at the outset of the war, the American forces were soon augmented by thousands of volunteers. These untrained soldiers tended to be undisciplined and poorly supplied, but the leadership of the American force performed with distinction. Scott and Taylor, the two ranking officers in the U.S. Army had similar experiences, both had fought in the War of 1812, the Black Hawk War, and the Seminole Wars. In temperament and leadership style, they personified the dual nature of the American Army. Taylor, dubbed “Old Rough and Ready” by his soldiers, cared little for drill and polish, but stood ready for combat at a moment’s notice. He had adopted many of the habits of the frontier troops under his command, and his campaigns were characterized by extremely aggressive operational maneuvers and a preference for the tactical defensive. In contrast, Winfield Scott, called “Old Fuss and Feathers,” was noted for his insistence upon proper discipline and appearance within the ranks. He adopted a more methodical approach to warfare, conducting a traditional siege of Veracruz, and moving directly inland toward the capital, Mexico City.

Taylor’s advance onto what was unquestionably Mexican soil commenced in the summer and autumn of 1846. Taylor reasoned that the capture of Monterrey, the second largest city in Mexico, would compel Santa Anna to renounce any claims to the disputed region. Monterrey was defended by 7,500 troops and several dozen artillery pieces, while Taylor commanded a force of only 6,200 and no heavy guns. Rather than settling into a traditional siege, Taylor divided his forces, planning to simultaneously attack from east and west. Had the Mexican commander of the city’s garrison, Pedro de Ampudia, been more gifted, Taylor’s army might have been defeated in detail. Instead, Ampudia decided that he could not hold the city, and he petitioned for an armistice. Taylor agreed to take possession of the city after allowing the Mexican forces to march out intact, infuriating President Polk, who thought the American general should have some how captured or destroyed the defending army. He ordered Taylor to renege upon the deal, but Taylor ignored the order and allowed the Mexican garrison to withdraw.

While Taylor marched on Monterrey, small bands of American cavalry began to advance into and through modern New Mexico, Arizona, and California. These units met little resistance, and essentially captured the territories without a fight, primarily by showing the American flag and announcing victory. After these conquests, these groups moved to join Taylor’s forces in Northern Mexico, anticipating an advance upon Mexico City. American units had secured the Texas, New Mexico, and California regions, established a successful blockade of the Mexican coast, and moved an army into Mexico to occupy a major city. The one objective they had not achieved was convincing the Mexican government to sue for peace terms.

Mexico had no intention of giving up half its territory, and in early 1847, Santa Anna embarked upon a plan to drive the invaders out. He learned that Polk had ordered Scott to attack Veracruz from the sea, with the intent of marching directly upon the capital. To avoid the yellow fever season, Scott needed the invasion to begin early in the spring, and thus he could not await new volunteers to be trained and shipped to the theater. Accordingly, he removed more than half of Taylor’s force, including most of the battle veterans, in anticipation of the campaign season. To take advantage of Taylor’s weakness, Santa Anna marched an army of 15,000 troops through 300 miles of desert, planning to reoccupy Monterrey and destroy the invaders. Since the capture of the city, Taylor had done little to secure his position, and he was quite surprised to receive a surrender demand on February 23, 1847. He refused the demand, and despite being outnumbered more than three to one, took 4,500 green troops into combat against seasoned Mexican regulars.

Rather than remaining on the operational defensive, Taylor moved his unit to Buena Vista and hastily erected fieldworks. This provided the advantage of fighting a defensive battle in very rough terrain. Remarkably, his troops fought like veterans, making up for numbers with superior technology. Taylor’s field artillery units moved their guns to within one hundred yards of the enemy, firing canister rounds at point-blank range into densely-packed Mexican infantry. A unit of American sharpshooters armed with rifles devastated the enemy leadership, particularly mounted officers, the superior range of the rifles allowed accurate fire more than 300 yards. The Mexican army, after inflicting heavy casualties but absorbing even more, panicked and fled the field, leaving behind thousands of comrades to be captured. Santa Anna had failed to dislodge Taylor, and had allowed Scott a free hand in preparing to besiege Veracruz.

On March 9, 1847, ten thousand American soldiers and marines conducted an unopposed amphibious landing outside Veracruz. They quickly moved into positions to besiege the city, while the U.S. Navy began to shell the harbor defenses. After three weeks, the city capitulated, allowing Scott control of the port facilities to resupply his army. Knowing that the onset of fever season loomed, Scott ordered his forces to move inland, maintaining a supply line to the coast. Although he was able to move most of his combat troops away from the lowlands, a significant portion of Scott’s army remained on garrison duty, and proved extremely susceptible to tropical diseases. Malaria and yellow fever spread through the American army, decimating the forces.

With both Monterrey and Veracruz in American hands, it is possible that Polk expected Santa Anna to capitulate. Instead, the Mexican general marched his army back to Mexico City, and shifted his attention to halting Scott’s advance. Knowing that Scott would follow the National Highway into the Mexican interior, Santa Anna established blocking positions at a rocky gap named Cerro Gordo. He hoped to lure Scott into an ambush, attacking the American column as it moved through a narrow defile. However, at Cerro Gordo, Captain Robert E. Lee scouted a route around the enemy positions. By leading troops in a flanking movement across extremely rough terrain, Lee reversed the trap. American soldiers opened enfilading fire upon the Mexican positions, routing their numerically superior army and driving Santa Anna back into the capital.

At almost the moment of Scott’s triumph, he faced a new tribulation. Approximately one-third of his volunteers had reached the end of their enlistments, and refused to remain with the invading force. He had no choice but to allow their departure, leaving him dangerously short of troops. To augment his field force, Scott made the precipitous decision to abandon his supply lines and drive directly upon the capital while calling for reinforcements from the continental United States.

In August, 1847, Scott advanced upon Mexico City from the south, leading an army of nearly 11,000. He faced a combined Mexican garrison of more than 25,000 who had moved into fortified positions astride the approaches to the city. However, Scott compensated for his lack of numbers with the skillful use of large artillery pieces, battering holes in the defensive positions at Contreras and Churubusco. In the two battles, Mexican casualties topped 10,000, in contrast, American losses totaled only 1,000 troops. Out of fear that the Americans might assault the city from multiple directions, Santa Anna could not concentrate all of his forces out of a single location. By dividing his units, he opened his army to defeat in detail.

In desperation, Santa Anna offered an armistice, which Scott perceived as the precursor to a peace negotiation. In reality, Santa Anna used the respite to reform his army and renew his defenses. Scott’s response was to renew the assault, launching the battles of Molino del Rey on September 11 and Chapultepec on September 12-13. Once again, artillery smashed through the fixed defenses, opening gaps for advancing infantry columns. On September 14, American troops entered Mexico City and commenced an occupation of the capital. Amazingly, this did not provoke a surrender, Mexican forces continued to resist American control, particularly in the countryside.

In the United States, a faction of Polk’s cabinet began to push for the complete subjugation and assimilation of Mexico. In April, 1847, Polk had dispatched Nicholas Trist to negotiate with the Mexican government to end the war. Five months later, Trist still awaited a sign that any national authority was willing to negotiate. By the time Scott captured the capital, there simply was no national government left to capitulate. Scott became the de facto dictator of Mexico, working to restore order and civil services within the capital, while Trist sought any diplomatic overtures. Frustrated with the rising costs of the war, Polk ordered Trist to cease any negotiations and return to the United States.

Fortunately, Trist ignored the president’s order and finalized negotiations with the newly-constituted government of Mexico. On February 2, 1848, the Treaty of Guadalupe Hidalgo was signed, ceding the modern southwest to the United   States in exchange for approximately $18 million. Virtually no American politician embraced the treaty, some wanted more land, some less, and many thought Trist had no right to negotiate after his recall. Naturally, with nobody truly satisfied, the Senate ratified the document with minimal hindrance, formally ending the state of war.

The war had far-reaching consequences upon the American military. The Navy had successfully blockaded a massive enemy coastline, capturing and holding supply bases upon its length to support operations. The Army had engaged in a war of conquest over more than one million square kilometers, holding the major cities of Mexico and winning every significant engagement. Many of the most prominent American Civil War commanders, Union and Confederate, saw service in the war, and incorporated its lessons into their decision-making in the later conflict. A significant portion of these officers represented a new breed of professional in the American military, the West Point graduate. As Winfield Scott later stated, and thousands of new cadets have subsequently memorized,

“I give it as my fixed opinion, that but for our graduated cadets, the war between the United States and Mexico might, and probably would have lasted some four or five years, with, in its first half, more defeats than victories falling to our share; whereas, in less than two campaigns, we conquered a great country and a peace, without the loss of a single battle or skirmish.”

The war was the first successful war of conquest on foreign soil for the United States, but it was also the deadliest war in American history, as a percentage of forces engaged. Almost 15,000 troops died, though less than 1,500 died in battle or as a result of wounds. The results of the war opened a vast territory for the expansion of slavery, and the California petition for statehood in 1850 created the necessary conditions to overturn the Missouri Compromise, unbalance the Senate, and hasten onset of the Civil War.

The ramifications of the war are still felt today, particularly with the current hot-button political issue of immigration from Mexico. The war’s effects are felt on both sides of the border, for decades, the so-called reconquista movement has argued that through immigration, native peoples can reclaim the American southwest from European-descended dominance. For modern students to understand the current geopolitical climate of North America, it is absolutely vital that they understand the causes and results of the Mexican War on its own merits, not solely as a precursor of the American Civil War.