M6D2: “Our Manifest Destiny”: Westward Migration And The Mexican-American War

This discussion addresses the following outcomes:

  • Define the concept of “Manifest Destiny” and examine its role in  American expansionism into Texas and other Mexican territories. (CO#1, #3)

Expansion is a major theme of the United States’ history. As a young,  energetic country, the United States also saw itself as gifted by  Providence to spread out into neighboring lands. The migration of  Americans into Mexican territory opened a new chapter in that story.  Texan independence from Mexico seemed to fulfill the promise of Manifest  Destiny, not just in terms of land but in the spread of American  ideals. However, the Mexican-American War and westward migration did not  benefit all.

In preparation for our discussion be sure to read the Module Notes, Chapter 12: “Manifest Destiny (Links to an external site.)” and the following primary sources: John O’Sullivan Declares America’s Manifest Destiny, 1845,  (Links to an external site.)Cherokee Petition Protesting Removal, 1836, (Links to an external site.) and Chinese Merchant Complains of Racist Abuse, 1860. (Links to an external site.)

 (Links to an external site.)Using the primary and secondary source materials above as evidence, consider the following in a post of at least 250 words: (Links to an external site.)

  • What was the concept of Manifest Destiny? How did it rationalize  westward migration, US expansion into Mexican territories, the  Mexican-American War, and the Monroe Doctrine?
  • Choose one of the following groups and consider how the changes to  the west in this era affected their circumstances: American migrants,  displaced Native Americans, Chinese immigrants, Mexicans in the acquired  territories, or slaves

1. Westward Expansion

The tensions over slavery factored into other aspects of American politics and society, including westward expansion. Slavery was not the sole reason for American expansion. A common thread running through the country’s history has been its expansion westward. The War of 1812 resulted in Britain discontinuing its attempts to subsidize or support Native American tribes in the Ohio Valley or the Mississippi River Valley. This action helped secure the US’s ability to move westward, buying out or otherwise removing Native American tribes who inhabited the area. The removal did not go without controversy, as the several US wars with Native American tribes attest.

The United States’ geographic location was an immense help in its movement westwards. Flanked by oceans, the United States had little fear of external invasion (with the exception of Great Britain in the War of 1812). Nor did the early presidents favor intervention in foreign politics. The Monroe Doctrine (Links to an external site.) of 1823 established that the US would not interfere in European colonies currently in existence in the Americas, but would not tolerate further European intervention or interference in the western hemisphere. The Monroe Doctrine had little practical effect in deterring European behavior, but neither did foreign countries press the matter.

Peace with Britain was another advantage for the United States. The Treaty of Ghent opened the door for a US-British reconciliation of sorts: the US would no longer make moves to acquire British Canada, and Britain would not challenge US westward expansion in its commonly recognized borders. US-British relations were not perfect (particularly in the suppression of the international slave trade), but a series of treaties demonstrated US-British cooperation. The Rush-Bagot Treaty (Links to an external site.) of 1818 demilitarized the Great Lakes, established the current US-Canadian border west of the Great Lakes, and provided for joint occupation and government of disputed areas in the Oregon Territory. The Webster-Ashburton Treaty (Links to an external site.) of 1842 settled the Maine-New Brunswick boundary.



2. American Migration to Mexico and the Texas Revolution


To the south, the Transcontinental Treaty (Links to an external site.) of 1819 (also known as the Adams-Onis Treaty) established a firm US-Mexican boundary—first with Spain, then with the independent Mexico.  Ironically, it was the migration of American citizens out of the United States that set the stage for the most contentious stage of American expansion.

Following Mexico’s independence, Texas became part of the Mexican state of Coahuila y Tejas (the local name for the region). This area was in the far north of Mexico, and was sparsely inhabited. As part of a program to colonize the area, in the 1820s Mexico encouraged Americans settlers to migrate. Influential Americans like Stephen Austin (Links to an external site.) received large land grants to bring others to Texas and turn them into Mexican citizens.

Cotton, slavery, and American political ideals also accompanied the Texas settlers. Mexico’s abolition of slavery did little good—enslaved blacks were forced to sign lifetime contracts that undid the law’s intent. The tumultuous nature of Mexico’s politics also frustrated the acculturation process—white American settlers identified politically, religiously, and economically with the United States rather than with their new homeland. White Texans watched nervously as Mexico’s central government devolved into dictatorship and Mexico’s leadership threatened to bring Texas to heel. Mexico’s attacks on the Alamo (Links to an external site.) and Goliad (Links to an external site.) in 1836 backfired when Texas forces defeated Mexican troops at the Battle of San Jacinto (Links to an external site.), and secured their independence. Texas declared its independence from Mexico and Texans defended it while seeking annexation to the United States.



3. Manifest Destiny

Americans observed Texas’s fight with Mexico with interest. The Jackson and Van Buren administrations considered but then rejected annexation of Texas because of Mexico’s opposition as well as possible domestic controversy. Southern political interests hoped for annexation since Texas represented a vast slaveholding territory. Many Northern interests opposed annexation for exactly the same reason.


Americans both North and South considered not just Texas, but much of Mexico’s northern territories, as ripe for the taking. To them, the slave/free controversy was secondary to the intent of Providence, or “manifest destiny.” The concept of Manifest Destiny (Links to an external site.) was that the US “overspread the continent allotted by Providence for the free development of our yearly multiplying millions,” in the words of journalist John Louis O’Sullivan, who coined the term.

O’Sullivan’s exhortation included not just Texas, but Mexican California and the Oregon Country (then jointly occupied with Britain, a final disposition not yet resolved). It tied in with an American sense of purpose and exceptionalism, and of America’s commitment to progress and liberty. Mexico’s political turmoil and the battle it had lost against Texans seemed to confirm American exceptionalism. The presence of Native American tribes and their claims on the land did not inhibit the sense that expansion was inevitable and desirable.



4. Tension with Mexico, Compromise with Britain

Mexico’ government did not give up on recovering Texas after its declaration of independence. Not only did national pride play a role, but so did Texas’s expansive claims for its new boundaries, south to the Rio Grande and west into New Mexico. At the very least, Mexico expected the US to negotiate a final resolution. But the Texas issue was too hot for the Van Buren or Harrison/Tyler administrations to touch, so in the meantime Texas remained the Lone Star Republic.

The presidential election of 1844 (Links to an external site.) involved both the future of the Oregon territory and Texas. The Whigs nominated Henry Clay, who opposed Texas annexation in hopes of garnering Northern Whig votes. The Democrats nominated James K. Polk of Tennessee. Polk’s campaign was avowedly expansionist, and once Polk became president, he acted upon that impulse.


The decisive step toward the annexation of Texas preceded Polk’s inauguration. Outgoing President John Tyler requested that Congress pass a resolution of annexation, which required a simple majority, rather than a treaty which required the Senate’s consent and would fail due to Northern opposition. Annexation passed Congress by a close vote, and Texas became the twenty-eighth state. Abolitionists and other Northern politicians feared this represented the expansion of the “slave power” in national politics. By the terms of annexation, Texas would be included in the Missouri Compromise and any new states created from it (a significant possibility given its size) would be slaveholding states.

Mexico considered US annexation a breach of international law, a sentiment shared by many Northern Whigs already opposed to Texas’s admission as a slave state. Polk dispatched US military forces into Texas to defend the state’s expansive territorial claims. Such a move invited the inevitable response from Mexico.

Meanwhile, controversy over the Oregon territory also came to a head. Polk informed Britain that the US would end its joint occupation and would organize Oregon according to US claims, well above the Forty-Ninth Parallel (or as the slogan of the time went, “54’40 or Fight!”). This tactic was partially a bluff, designed to get Britain to compromise as the US was heading into conflict with Mexico. In fact, that’s exactly what Britain did in 1846.

Polk had secretly made offers to Mexico to resolve the Texas dispute, but such offers came too late and were likely to be rejected anyway. Fighting began in April 1846 when Mexican forces attacked US troops in the contested area. This attack gave Polk the justification to request a declaration of war, stating, “Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil.” Congress did declare war, but that did not mean the end of the debate.

“War fever” and patriotism sustained the war effort, but opposition was not insignificant. Northern Whigs were particularly opposed to the war. The Massachusetts legislature voted a resolution against it, declaring:

Resolved, That such a war of conquest, so hateful in its objects, so wanton, unjust, and unconstitutional in its origin an character, must be regarded as a war against freedom, against humanity, against injustice, against the Union, against the Constitution, and against the Free States; and that a regard for the true interests and the highest honor of the country, not less than the impulses of Christian duty, should arouse all good citizens to join in efforts to arrest this gigantic crime, by withholding supplies, or other voluntary contributions, for its further prosecution; by calling for the withdrawal of our army within the established limits of the United States; and in every just way aiding the country to retreat from the disgraceful position of aggression which it now occupies toward a weak, distracted neighbor and sister republic.

US forces—naval, the regular army, state militias, and volunteers—outperformed expectations. Northern Mexico was cleared of enemy forces within months. In California, US settlers overthrew Mexican authority and declared the Bear Flag Republic (Links to an external site.) in preparation for US annexation. US forces moved into New Mexico and soon occupied that region. By September 1847 US forces occupied Mexico City. But Mexico’s crippled government was so hostile to a settlement that the war continued on if only in name. It ended in early 1848 with the signing of the Treaty of Guadeloupe Hidalgo. The end result was that Mexico lost her northern territories (nearly half of her total land area) and the US grew by one-third.



6. The Wilmot Proviso Expands the Sectional Controversy


Northern Whigs largely opposed the war with Mexico. They were angry that Polk compromised on Oregon while fighting for Texas. Looking ahead, Whigs were concerned that future acquisitions like California might become slave states (since they were below the Missouri Compromise line) even though they had been free territory under Mexican law. The greater fear for many Northern politicians was that “free labor” was under attack.

Shortly after the Mexican-American War began, Representative David Wilmot of Pennsylvania wrote legislation to be attached to a war funding measure. The Wilmot Proviso (Links to an external site.) stated:

Provided, That, as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico by the United States, by virtue of any treaty which may be negotiated between them, and to the use by the Executive of the moneys herein appropriated, neither slavery nor involuntary servitude shall ever exist in any part of said territory, except for crime, whereof the party shall first be duly convicted.


Even though the Proviso failed to pass Congress, its introduction infuriated Southern politicians who saw it as an attack of slaveholding states and a violation of the Missouri Compromise. It angered Southern states against Northern states, and also made Southern Whigs and Democrats more suspicious of their Northern party counterparts. The grounds for sectional compromise were eroding, slowly but surely.



7. The Implications of Manifest Destiny


The principles of Manifest Destiny included not just a physical expansion of the United States, but an expansion of American ideals. In large measure, those ideals were based an American racial precepts. The Treaty of Guadeloupe Hidalgo assured Mexicans in now-US territory that they could remain and become US citizens, but many Americans considered that to be a right in name only. Mexicans in the Southwest found themselves in an American system that placed whites on top and denied others equal treatment. Similarly, Native American tribes in the Southwest faced more direct contact with American migrants who considered the land to be US-owned. The discovery of gold in California in 1848 (Links to an external site.) at Sutter’s Mill stimulated Chinese immigration to the region, along with thousands of Americans. This added another wrinkle to social relations and the issue of civil rights and liberties and these nineteenth-century precedents continued on well into the twentieth century.

The US victory in the Mexican-American War also stoked interest in further expansion. Southerners especially coveted Cuba, then a Spanish colony with a long history of tropical products and slavery. More ambitious Southerners engaged in efforts to establish an American presence in Central and South America. These largely failed, but demonstrates the durability of slavery and the ability of Southerners to plan for its expansion. These added to the sectional debate into the 1850s.