The Mexican American War

  By Decebal
Contents »
1. Introduction

The Mexican-American war of 1846-1848 is one of the defining moments in the history of the American West. Its significance has been overshadowed in popular imagination by the magnitude of the conflict that followed it, less than 2 decades later: the US civil war. This latter conflict has also made it difficult to evaluate and understand the exact consequences of the US Mexican War on the American West. The task of understanding the impact of this war is made even more difficult by other subsequent events occurring in that geographical area, such as the California gold rush, which have dramatically altered the demographics, economics, and hence the history of the region. One obvious way to understand the impact of the Mexican war on the West is to look at its immediate results and consequences of the war. Another way, more subtle, is to examine the impulses and motivations which have led to the war in the first place. As we will see, the various proponents of the war had some fairly precise motivations and goals which related to the geographical areas that were annexed by the US following their victory in the war.

We will therefore examine the impact of the US Mexican war on the American West, by examining the direct results of the war, but also by analyzing the motives and impulses which have led the United States to provoke the war with Mexico. The thesis of this essay has 3 parts. First, the United States ended up annexing the area which would benefit it the most economically and strategically, and which could be colonized the easiest without having settlers of European descent competing and intermixing with Mexicans, Indians and Blacks. Second, the annexed territories would have developed into slave states, as was the intent of the Southerners who pushed for the war, had it not been for the Civil War which erupted only 13 years after the annexation, and for the California Gold Rush. Finally, in the larger view of the American West, the war had the effect of modifying Western mythology by strengthening the American Westerners’ sense of their own infallibility and invincibility as compared to the supposedly inferior Mexicans and Indians. This was to play a role in the later interactions between these people and the American Westerners.

The direct result of the war was an overwhelming US victory, resulting in the annexation of a huge swath of territory, covering the current states of California, Nevada, New Mexico, Utah and most of Arizona. There have been numerous theories proposed as to why the US provoked the war and ended up annexing those particular areas. This essay will examine them and relate these theories to the implied consequences on this region of the West. The best known theory related the US-Mexican war is that this was a case of Manifest Destiny: in the view of Americans at the time, their God-given mandate to colonize the North American continent and bring American values and institutions to those areas. Another theory is that there was interest from the part of Southern states to provoke the war and annex these areas in order to transform them into slave-holding states, which would enable them to restore the balance of power with the North, which had been upset by the North’s population gains. By the Missouri compromise of 1820, any new states south of the 36th parallel would allow slavery [1]. Still other groups such as merchants and some politicians saw the war as an occasion to gain access to areas that could be ideal ports on the Pacific, notably the San Francisco and the San Diego bays, which could open up immense commercial opportunities. The question of why the Americans, following their decisive victory decided to annex only those areas mentioned above and not also more Mexican regions or possibly the entire Mexico, can be explained by economic reasons and by the racism of the American public, who did not want to annex areas heavily inhabited by a Mexican population which constituted of a mix between Europeans but also Native Americans and blacks. The war was also to have an effect directly and indirectly upon the American West, by changing the lives of the veterans that came from the West, and by adding to the mythology of the American West. All these aspects will have to be examined in order to gain a solid understanding of the US Mexican war and its consequences on the American West.

2. Prelude to War

The most logical place to start analyzing the impact of the US Mexican war is to briefly explore the war itself and some background which led to it. As we will see, there were numerous currents in the American political scene, which advocated war with Mexico. Texas, where the war would start, was a contentious issue. It had gained its independence from Mexico in 1836 and by April 1844, US representatives had secured a treaty of annexation. By June 1844, the US had sent a force under the command of General Taylor which was ready to protect the republic of Texas. However, the annexation treaty failed to pass through senate during that same month [2]. To complicate things further, this was an election year. Martin Van Buren, the leading Democratic candidate and Henry Clay, the permanent Whig contender, both issued carefully designed statements opposing annexation in a vain hope of excluding the divisive issue from the campaign. As a result of Van Buren’s statement, the southern delegates vetoed his candidacy and forced his replacement by the dark horse James Polk. Polk injected the question of Texas directly into the campaign by insisting on the “Reoccupation of Oregon and the reannexation of Texas”. That tactic forced Clay to modify his stand in order to hold some of his southern votes. This in turn alienated sufficient abolitionists to enable Polk to carry the presidency [3]. The election of Polk due to his aggressive stance on expansionism had set the tone of his presidency and had set him up for desiring a war with Mexico.

The annexation of Texas created an uproar in Mexico, who had not ever recognized the former’s independence. In an effort to avoid war, the Mexican president Herrera asked the US to send an envoy for negotiations. The US took this opportunity to send Slidell to make an unsuccessful attempt at purchasing territory. President Herrera personally opposed war with the US, but he was overthrown by the so-called Centralists, led by Mariano Parades on Jan 2, 1846. The Centralists were against a moderate foreign policy and actually may have desired war. Parades approved the massing of troops on the Texan border. The Americans now found a pretext to get Mexico to declare war. As far as Mexico was concerned, her boundary with Texas lied on the Nueces River. The Americans declared that the natural border of the Texas actually lied on the Rio Grande, further to the south, and sent troops to occupy the region between the 2 rivers. It is worth noting here that the Americans were concerned about appearances, and that they did their best to provoke Mexico into a war, without having to bear the responsibility of actually starting the war[4].

3. The War

The occupation of the region between the Nueces and the Rio Grande rivers was interpreted as an act of war by Mexico and by April 1846, hostilities started [5]. The Mexicans initially had a much larger army and expected a victorious war fought mostly in Texas [6]. However, after some initial setbacks at Palo Alto and Resaca de Palma, the Mexicans were forced to evacuate the strategic town of Matamoros and retreat to the south. The war came to a standstill, as the American army encamped at Matamoros swelled with volunteers. Meanwhile, in large part due to the initial defeats, political turmoil occurred in Mexico City. Eventually, the ex-dictator Santa Anna came to power. The Americans achieved another victory by General Taylor capturing Monterrey on September 25, 1846, after which he agreed to an eight week truce. By this time, President Polk and the American public had their expectations bolstered by the series of victories and Taylor had to break the truce early. Santa Anna personally led a large army aimed to recapture Monterrey, but he was defeated by Taylor at the battle of Buena Vista. The decisive moment in the war came with General Winfield Scott’s landing at the major port of Vera Cruz on March 11, 1847 [7]. His force went inland towards Mexico City and achieved a string of victories at Cerra Gordo, Puebla and Contreras. The battle for Mexico City was fought at Chapultepec, which is sometimes referred to as “the Halls of Montezuma”. As a result of the battles, Mexico City was occupied on September 13, and Santa Anna resigned his presidency on September 16, 1847 [8]. An American envoy, Nicholas Trist, concluded negotiations with the new Mexican government.

Of particular interest to us is the war in the western borderlands. Immediately after the declaration of war, General Kearny was ordered to occupy New Mexico and California. Under his command, the “Army of the West”, which consisted largely of Missouri volunteers and numbered fewer than 2,000, moved down the Santa Fe Trail into New Mexico. Kearny entered Santa Fe unopposed on Aug. 18, 1846. Peaceful trade and commerce in the preceding years had greatly eased the conquest of New Mexico. After establishing a civil government, Kearny divided his command into three groups: one, under Sterling Price, occupied New Mexico; a second, under Alexander William Doniphan, captured Chihuahua; the third, under his own command, headed for California. Kearny set out for California on September 25 with only 300 dragoons. At Socorro, N. Mex., they met the famous guide Kit Carson, who was returning from California. Learning that the conquest of California was virtually complete, Kearny sent 200 of his men back to Santa Fe and, led by Carson, continued to California [7].
The American settlers in California had revolted against Mexican rule and established (June 1846) the Bear Flag Republic, under John C. Fremont. On July 2, U.S. Commodore John Drake Sloat landed at Monterey. He proclaimed U.S. jurisdiction on July 7 and two days later occupied San Francisco. However, California was by no means under U.S. control. Commodore Robert Stockton, who replaced Sloat on July 23, sailed down the coast and landed troops under Fremont at San Diego and others near Los Angeles. Stockton had to coordinate his troops with those of Kearny, to occupy Los Angeles and San Diego, which had been occupied by a Mexican rebel force. On January 13, Fremont received the final surrender of the rebels and signed the Treaty of Cahuenga. After a bitter dispute among Stockton, Fremont, and Kearny, the latter established a provisional government in California [10].

At the end of the war, Trist negotiated the Treaty of Guadalupe Hidalgo with the Mexican government. Even though his negotiations were not authorized, they were eventually approved by Congress. By virtue of the treaty, Mexico recognized the annexation of Texas, and ceded the territory corresponding to California, most of New Mexico, Nevada, Utah and Arizona. Altogether, these territories amounted to about 3.1 million square kilometers, which was more than half of Mexico. This was the most spectacular conquest in the history of the United States, and indeed one of the most spectacular in the history of the world.

4. Was it Manifest Destiny?

The term “Manifest Destiny” was coined by John O’Sullivan in 1845, and was used on occasion during the 1840’s to justify the American expansionist policy in the West and beyond. The term was actually used much more widely by historians in the two decades following the Second World War [11]. The idea was that the United States had a “Manifest Destiny” given by God, to expand across the Western Hemisphere, a mission to spread the American ideals of freedom and democracy to the supposedly inferior and uncivilized peoples of the American West and Latin America. An associated idea is that of a “land hunger”, as this period is characterized by the acquisition and colonization of territories by Europeans across the world. The ideals of “Manifest Destiny” supposed to be spread were thought to be typically American, as visitors to Europe had remarked on the appalling living conditions of European workers, to which supposedly even the living conditions of the American black slaves were preferable [12]. The influential editor Bennett of the New York Herald believed that Europe was too distressed to oppose America’s expansion in the West [13]. To the expansionists who believed in Manifest Design, the expansion of the United States is described not so much in terms of what the territorial acquisitions would do for the country but what the country would do for those new territories.

As Thomas Hietala notices, the expansionists relied on other self-serving beliefs to explain and justify territorial acquisitions. They perpetrated the convenient myth of a vacant continent, invoking the image of North America as an uninhabited, howling wilderness that the new chosen people had transformed from savagery to civilization during their predestined march to the Pacific. Others recognized that the continent was not empty and that Indians and Mexicans had occupied much of it prior to American ascendancy but stressed that the United States, in seeking to expand, sought only what was best for those dispossessed races. Unlike the exploitative Spanish, who had first encountered non-white natives in the trans-Mississippi West, Americans in the nineteenth century came to indigenous peoples as missionaries, not conquistadores [14].

This may have been the view of a large part of the American public, and even that of some politicians. But the people in positions of power were much more pragmatic. President Polk for example, was much more concerned with the economic value that the newly acquired territories would bring to the United States. The California ports, he said, “would in a short period become the marts of an extensive and profitable commerce with China and other countries of the East” [15]. This view was echoed in the reasoning of the few politicians, merchants and travelers who could appreciate California’s significance. In fact, the purchase of California for as much as 50 million dollars was contemplated at the time [16]. As for the acquired territories, after the end of the war, Polk predicted that “in this vast region, whose rich resources are soon to be developed by American energy and enterprise, great must be the augmentation of our commerce, and with it new and profitable demands for mechanic labor in all its branches and new and valuable markets for our manufactures and agricultural products” [17]. It is clear that he was much more concerned with the economic opportunities for the new territories and with their commerce with the already established areas of America than with the noble mission of bringing civilization to the West. It is also unlikely that he was alone in establishing this order of priorities, since most people in a capitalist system are profit driven. Another factor which played a role was the Americans’ fear of losing California to Britain or France, which both had designs on that rich and relatively uninhabited land [18]. The other lands annexed by the US were not even close to California in economic potential; however, their annexation was necessary for strategic reasons, even with the annexation of the Oregon in 1846, as an uninterrupted band of land across to the Pacific would have strengthened the US hold on California.

If the ideas of Manifest Destiny had been the predominant driving force behind the US Mexican War, then the Americans would have had no real objections to the colonization of the entire Mexico, especially since the Americans had won a sound victory, and most of Mexico was under American military occupation. What better way to bring American ideals to a people? Indeed, there were some who advocated the annexation of “all of Mexico” [19]. However, this was not the case. The Americans were primarily interested with those areas which presented the greatest economic potential, namely California and Texas. As we have seen above, the annexation of the other areas which they acquired was necessary to connect California with the rest of the United States. While some have argued that the Mexican government would have never agreed to the cession of even larger territories than were eventually annexed, that would not have stopped the Americans from annexing the entire Mexico, since they controlled militarily the entire country. One possible reason is the opposition of Southern groups, who while they had advocated war with Mexico, they did not deem southern Mexico suitable for the culture of cotton, and did not therefore think that slavery would flourish there [20]. In addition to economic reasons, there was another reason which deterred the Americans from annexing more of Mexico than they did, or the entire Mexico altogether.

That reason is racism. Anti-Mexican prejudices were widespread among Americans, although not universal. Illinois congressman Orlando Ficklin described Mexico’s heterogeneous population as “barbarous and cruel”, “a sordid and treacherous people”, who were “destitute of noble impulses” [21]. The administration’s assumption that the Mexicans would not fight (and its outraged assertion, when the Mexicans did fight, that their attack was treacherous and unprovoked) reflected an underlying assertion that the Mexicans were an inferior people [22]. In June 1846, the New York Herald’s editor, Bennett, attributed “the imbecility and degradation of the Mexican people” to “the amalgamation of the races” there and predicted an early triumph for the United States. He observed that “the idea of amalgamation has always been abhorrent to the Anglo-Saxon race on this continent” [23]. In political circles, there were two trains of thought: one that Mexico should be annexed completely and that the Mexicans would be assimilated, and the other that only those regions which were relatively uninhabited should be annexed, in order not to introduce too large of an “inferior” element to the United States population. In the end, it was the latter idea that carried the day.

To summarize, the ideals of Manifest Destiny, those of carrying forth American ideas of democracy and freedom to the people of the Western hemisphere, only had a limited impact on the annexation of northern Mexico. More important were the pragmatic motives that were really behind Manifest Destiny, and which President Polk was interested in: the acquisition of new territory where to develop agriculture and industry, the opening of new markets, the securing of good ports on the Pacific for trading with Asia, and ensuring that a continuous band of territory united the Eastern US to the Pacific, for strategic reasons. Also important in deciding which territories to annex, were racial and demographic concerns, since the Americans wanted territories which were relatively uninhabited by people they considered inferior, such as Indians, blacks and Mexicans.

5. The Southern Plot and Slavery in the West.

By the time of the Mexican War, the Southern states had lost a lot of ground in terms of power relative to the North. This was due to the greater population and industrialization of the northern states. This loss in relative strength was also apparent in national politics: the Northern states had more seats in Congress. According to the Missouri compromise of 1820, any new states south of the 36th parallel would allow slavery. When the issue of the annexation of Texas was discussed, the Southern delegates supported it wholeheartedly. Apparently, the plan was to carve four slave states out of Texas. This would have enabled the South to maintain control of the Senate, although the North would have maintained control of the House [24]. The territories that were annexed after the Mexican war, and for that matter all of Mexico, were south of the 36th parallel. Any new states carved out of Mexican territory would have become slave-holding states as well, further tipping the balance to the Southern side. This was even though Mexico had abolished slavery in the late 1820’s, and all annexed Mexican land was free territories.

The extent to which the political pressure from the Southern states would determine US diplomacy can easily be seen in these remarks made by the US commissioner during the treaty negotiations. During the progress of the negotiations, Mexico begged for the insertion of an article providing that slavery should not be permitted in any of the territories ceded. The US commissioner replied that: “the bare mention of the subject in a treaty was utter impossibility; that if the territory should be increased tenfold in value, and besides, covered all over a foot think with pure gold, on the single condition that slavery should be excluded therefrom, he could then not even think for a moment of communicating it to the President. The “invincible Anglo-Saxon race” could not listen to the prayer of “superstitious Catholicism goaded on by a miserable priesthood”, even though the prayer was on the side of justice, progress, and humanity.”[25]. Since the commissioner represented the interests of his country to the best of his knowledge and abilities, it was clear that the annexed territories were meant to be converted into slave-holding states.

Some historians have argued that there was no such Southern plot to create additional slave-holding states. They point out that some Southern politicians were against annexing Mexican territories, because most of them would be unsuitable to cotton production [26]. However, they probably were a minority as evidenced by the failure to include the Wilmot Proviso in the final peace treaty. A minor Democrat from Pennsylvania, David Wilmot offered an amendment which declared that slavery should be prohibited in any territory acquired from Mexico. A bloc consisting mostly of Whigs and Northern Democrats passed the amended bill. But a filibuster developed in the Senate (where the Southerners were still powerful), and Congress adjourned without further notice [27]. The Southerners had blocked the Wilmot Proviso.

The annexed territories were therefore to have become slave-holding states. However, most of the territories only became states after the Civil War erupted in 1861. The only one that did become a state before the war, California, created its own laws against slavery when it entered the Union. These laws were instituted primarily because the gold miners were worried about competition from slave-owners, and even then, were not always enforced [28]. If not for the gold rush and the civil war, one might easily envision the new states which resulted from the annexed Mexican territories, becoming states that allowed slavery.

6. The American Westerners and the War

The population of the West seemed to support the war much more whole-heartedly than that of other regions of the United States, perhaps with the exception of the South. Nowhere is that more evident than in the number of volunteers for the war: out of a total of 69540, 40000 were from strictly Western states and 17320 were from the sparsely populated Northwest; while from all the northern states, with a population twice as great and wealth many times greater, only 7930 volunteers offered. An imbalance existed for regular soldiers as well. With a population of 4.7 million, the Northwest sent nearly 25,000 soldiers to the front, while the whole North, from Maryland to Maine, with a population of 9.3 million, furnished only 27,000. The Southwest, including Kentucky and Missouri, had according to the same census of 1850, 4,985,000 people, of whom at least one third were black slaves, but from these lower Mississippi states there went more than 45,000 soldiers [29]. This disproportionate contribution to the war could not have been made by the Western states without widespread support from both the population, as evidenced by the number of volunteers, as well as support form the state governments, as evidenced by the comparatively large number of regular soldiers. The large number of soldiers coming from the West was also bound to have a lasting effect upon this region, as this would create a pool of numerous veterans who undoubtedly play an important role in the future development of the region. As a general rule, war veterans often become successful in politics or business, to say nothing of the veterans who would continue with a career in the army. The veterans who would become elected officials or successful businessmen would certainly have a different vision of the world after the war, so Western states were undoubtedly affected by the Mexican war in this indirect way.

Aside from the consequences of the war upon Westerners who fought or were connected somehow to soldiers who fought in the Mexican War, the war also had an undeniable effect upon the way Westerners viewed the Mexicans and by extension other people such as the Native Americans. We can see this as an effect upon the mythology of the American West. This change in perspective had a lot to do with the way the Americans desired to view themselves. The US Mexican War, as the first war the Americans fought on foreign soil, had a romantic and defining quality for the American public. In the words of Nathaniel Hawthorne: “With a spirit of romantic adventure, America’s peaceful citizens sought by daring and desperate valor, to prove their fitness to be entrusted with the guardianship of their country’s honor” [30]. As the war went very well for the Americans, better than anyone expected, a whole stock of literature developed around the war, prose and poetry along with the numerous newspaper articles.

Although the bravery of the Mexicans was sometimes noticed, so as not to belittle the achievements and character of the American troops, who had to have defeated a somewhat worthy opponent, in general the Mexicans were not very well portrayed. For example, in a Mobile newspaper, the Mexicans were said to be “inferior in virtually every element of success”. It was charged that Mexican army officers secured their commissions through political influence or bribery, and were often men of corrupt morals and dissipated habits. Mexicans were at times even compared unfavorably with slaves in the American South [31]. Whether the supposed inferiority of Mexicans was attributed to racial differences, as the majority believed, or to the corruption of its political, military and religious differences, as others maintained [32], the fact remains that the perspective of the Mexicans in American imagination following the war, changed for the worse. Whereas before Mexico had a rather romantic quality in popular imagination, and the country and its people were respected as worthy rivals [33], after the war, the perception changed to give way to a general attitude of contempt and a complex of superiority which remains to this day imprinted in the American popular consciousness. This was to influence the lives of Hispano-Americans and cross border relations for the remainder of the history of the American West.

Conversely, the Americans’ view of themselves changed as well. The easy victories over the Mexicans had convinced the Americans that they were somehow superior to the Mexicans and that the United States was the greatest country in the world. This attitude was strongest in the soldiers who had fought in the war. In the words of a Pennsylvania volunteer: “Mexico is no doubt one of the best places in the world for an American to feel proud of his nationality” [34]. As we have seen before, a disproportionate amount of soldiers came from the American West, so this change in attitude and popular perception must therefore have been especially pronounced over there. Since the Mexicans, as a “mixed race”, were considered to be superior to Native Americans, this change in perception must have accentuated even further the racism and the superiority complex of Americans towards Native Americans. We might say therefore that the war had the effect of modifying Western mythology by strengthening the American Westerners’ sense of their own infallibility and invincibility as compared to the supposedly inferior Mexicans and Indians

7. Conclusion

The US Mexican war was a conflict which was precipitated by various interest groups in the United States. The reasons why these interest groups desired war are reflected in the aftermath of the war. This aftermath was a major US victory, which resulted in the annexation of a huge portion of land, covering the current states of California, Nevada, New Mexico, Utah and most of Arizona. These areas were annexed because they would have benefited the United States from an economical and strategic point of view, and they could be colonized the easiest without having American white settlers competing and intermixing with Mexicans, Indians and African Americans. The annexed territories were to have developed into slave states, as was the intent of the Southerners who pushed for the war, had it not been for the Civil War which erupted only 13 years after the annexation, and in the case of California, the Gold Rush of 1849. In the larger view of the American West, the war had the effect of strengthening the American Westerners’ sense of their own infallibility and invincibility as compared to the supposedly inferior Mexicans and Indians. As most of the soldiers who fought in the US- Mexican war were Westerners, this was to play a role in the later interactions between Westerners and Mexicans as well as Native Americans. The consequences of the US-Mexican war are still felt to this day throughout the American West.


1. Thomas R. Hietala, “Manifest Design: American Exceptionalism & Empire”, p 210
2. Dean B. Mahin, “The Olive Branch and the Sword: The United States and Mexico, 1845-1848”, p 31
3. Jack Bauer, “The Mexican War 1846-1848”, p7
4. Glenn W. Price, “Origins of the War with Mexico: The Polk-Stockton Intrigue”, p 100
5. Mahin, p. 63
6. Jose Maria Roa Barcena, “Recuerdos de la Invasion Norteamericana (1846-1848)”, v1 p 55
7. Ibid, pp 260-282
8. Bauer, pp 313-326
9. Ibid, pp 134-159
10. Ibid, pp 183-196
11. Hietala, p 255
12. Ibid, p.121
13. Ibid, p.120
14. Ibid, p132
15. President James K. Polk’s 3rd annual address (Dec 7, 1847)
16. Norman A. Graebner, “the Land-Hunger Thesis Challenged”, p53 (part of Ruiz- “The Mexican War”)
17. President James K. Polk message on the treaty with Mexico (July 6, 1848)
18. Hietala, pp.73-78
19. Ibid, p.163
20. Chauncey W. Boucher, “The Conspiracy Denied”, p 25-27 (part of Ruiz- “The Mexican War”)
21. Hietala, p.153
22. Ibid, p.154
23. Ibid, p.156
24. James Ford Rhodes, “The Conspiracy Thesis”, p11 (part of Ruiz- “The Mexican War”)
25. Ibid, p17
26. Chauncey W. Boucher, “The Conspiracy Denied”, p 18-28 (part of Ruiz- “The Mexican War”)
27. David M. Pletcher, “The Diplomacy of Annexation: Texas, Oregon and the Mexican War”, p. 460
28. Andrea Franzius, "California Gold -- Californian Nativism and Racism"
29. William E. Dodd, “Western Responsibility”, p 40-41 (part of Ruiz- “The Mexican War”)
30. Robert W. Johannsen, “To the Halls of the Montezumas: The Mexican War in the American Imagination”, p 68
31. Ibid, p 23
32. Ibid, pp 23-24
33. Ibid, pp 144-145
34. Ibid, p173