Rivalry Along the Rio Grande: War with Mexico

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Rivalry Along the Rio Grande: War with Mexico


Tensions. After 1845 the fact that Texas was now part of the United States was beyond dispute. Yet annexation did not calm tensions since the Texas-Mexican border remained a subject of dispute. The Mexican government defined the south and west border of Texas at the Nueces River. The Texas government, now backed by the U.S. government, declared that the Rio Grande was its southern border, a claim that increased the size of Texas by almost 200 percent. Predictably, Mexico responded to the Texans belligerent declaration by breaking off diplomatic ties with the United States. This move set in motion a series of events that changed the pattern of Western expansion, foreign relations with Mexico, and American politics.

President James K. Polks War Message

Elected on a platform promising to expand the United States westward, James K. Polk of Tennessee wasted no time provoking a war with the Republic of Mexico over territory. With his eyes on California and New Mexico, Polk sent an envoy to Mexico City with an offer to purchase the territory. At the same time, he ordered American troops into disputed territory near the border, hoping to taunt Mexican soldiers into an attack. When the attack failed to materialize, Polk decided to declare war on Mexico anyway. On 9 May 1846, however, the day he planned to send his declaration to Congress, Polk learned that eleven U.S. soldiers had been killed by Mexicans in the disputed area. He quickly rewrote his declaration of war, excerpted here:

The existing state of relations between the United States and Mexico renders it proper that I should bring the subject to the consideration of Congress....

The strong desire to establish peace with Mexico on liberal and honorable terms, and the readiness of this Government to regulate and adjust our boundary and other causes of difference with that power on such fair and equitable principles as would lead to permanent relations of the most friendly nature, induced me in September last to seek the reopening of diplomatic relations between the two countries. The Mexican government not only refused to receive him or listen to his propositions, but after a long-continued series of menaces have at last in vaded our territory and shed the blood of our fellow-citizens on our own soil.

The grievous wrongs perpetrated by Mexico upon our citizens throughout a long period of years remain unredressed, and solemn treaties pledging her public faith for this redress have been disregarded. A government either unable or unwilling to enforce the execution of such treaties fails to perform one of its plainest duties.

Upon the pretext that Texas, a nation as independent as herself, though proper to unite its destinies with our own she has effected to believe that we have severed her rightful territory, and in official proclamations and manifestoes has repeatedly threatened to make war upon us for the purpose of re-conquering Texas. In the meantime we have tried every effort at reconciliation. The cup of forbearance had been exhausted even before the recent information from the frontier of the Rio Del Norte. But now, after reiterated menaces, Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil. She has proclaimed that hostilities have commenced, and that the two nations are now at war.

As war exists, and, notwithstanding all our efforts to avoid it, exists by the act of Mexico herself, we are called upon by every consideration of duty and patriotism to vindicate with decision the honor, the rights, and the interests of our country.

Source: Sean Wilentz, ed., Major Problems in the Early Republic (New York: Heath, 1991).

The Oregon Question. In 1844 Democrat James K. Polk had run for president on a platform that called for the immediate annexation of Texas and a border for the Oregon Territory that reached north to 54°40, the boundary with Russias settlements in Alaska. However, he secretly wished for more than Oregon and Texas: he coveted Mexican California and New Mexico as well. Texas annexation was accomplished even before Polk entered

the White House; Oregon was another matter. Both England and the United States had agreed in 1818 to occupy the Oregon Country jointly, with the understanding that a future treaty would decide what part of the territory would become American and what would become part of Canada. By 1845 there was talk of war by both Britain and the United States over the Oregon boundary. In fact, one of the catchiest Democratic slogans during the 1844 election was Fifty-four forty or fight! (a reference to the latitude where expansionists hoped to draw the northern boundary of the territory), suggesting that Oregon was worth a war with Great Britain.

Peaceful Resolution. President Polk, contrary to the bellicose promises of candidate Polk, was not willing to go to war with Britain over Oregon. Instead he accepted a treaty in 1846 that drew the territorial border at the Forty-ninth parallel, the current United States-Canadian boundary. Some Northern Democrats were upset that they had supported Polks efforts to make the Rio Grande the Texas border, which expanded territory under control of slaveholders, and then signed away one-half of Oregon, territory they believed would have been for free farmers only.

Provoking a War. Polk, meanwhile, was busy plotting how to gain the rest of the Mexican northwest for the United States. His first move was to send an envoy to Mexico City with an offer to purchase California and New Mexico, an acquisition that would mean the loss of half of Mexicos territory, for $30 million. At the same time, he ordered American troops into the disputed territory between the Nueces and Rio Grande, and he dispatched a naval squadron into the Gulf of Mexico. Polk also attempted to stir up pro-American sentiment among the settlers in central California by naming a popular businessman from Monterey American consul and starting talk about California becoming the thirty-first state. Then Polk sat back and waited for any of these forms of provocation to prompt the Mexicans to fight back. When they did not respond as he had anticipated, Polk decided to declare war on Mexico anyway. On 9 May 1846, however, before he took action on his own, Polk received word that Mexican soldiers had crossed the Rio Grande and killed eleven Americans patrolling the disputed area. He sent the official declaration of war to Congress two days later.

Conflict. The declaration of war ran into trouble in Congress, where Whigs, most of them from Northern states, tended to oppose both continued westward expansion and war with Mexico. Nevertheless, in the end most of them voted for the declaration rather than be branded unpatriotic. As a result the declaration of war passed the House by a vote of 174-14 and the Senate by 40-2. Many Whigs at the time remembered how the Federalist Party had openly opposed the War of 1812 and never recovered politically; despite their misgivings, they voted for war.

Slavery and Expansion. The American people were far from united on the subject of the war with Mexico. Many Northerners feared that slavery would spread into the fertile lands gained as a result of the war, reversing Mexicos abolition policy. Most Southerners, for their part, hoped that future American settlers would be able to take their slaves into the new Western lands. After all, a large majority of the soldiers fighting in the war came from the South. Besides, they reasoned, Americans were free to take their property wherever they wished.

Northern Fears. The slavery issue quickly became intertwined with war aims in the U.S. Congress. For years a small but growing number of concerned Northern congressmen had watched while proslavery Democrats invoked party unity to table antislavery petitions, bar abolitionist material from the mails, and expand the scope of the peculiar institution into the new state of Texas. To be sure, even those Northern Democrats who opposed slavery were often more than willing to repress abolitionism in order to maintain the Jacksonian coalition in both North and South. By the mid 1840s many of these politiciansincluding those with impeccable Democratic recordsbegan to believe that Southern encroachment had outstripped the benefits of coalition.

Wilmot Proviso. In August 1846, during the early stages of the war with Mexico, President Polk requested $2 million from Congress to facilitate peace negotiations and, if possible, buy California and New Mexico. Northern Democrats saw the bill as an opportunity finally to thwart their Southern brethren, who appeared poised to snatch yet more territory for slavery. On 8 August, a first-term Pennsylvania representative named David Wilmot added a proviso to the bill that barred slavery from any territory acquired during the war. The amendment, known as the Wilmot Proviso, framed the national debate over slavery until the start of the Civil War.

Jeffersonian Precedent. Wilmot and his allies drew the language for the proviso directly from Jeffersons 1787 Northwest Ordinance. When it was his turn to speak, the freshman legislator endorsed the presidents request for funds. The House of Representatives passed the measure 87-64. Nearly all Northern representatives, Democrats and Whigs, voted in favor of the proviso; Southern Democrats and Whigs voted almost unanimously against it. In the Senate, which was dominated by Southerners, the measure was defeated.

Southern Countermeasures. To counter the Wilmot Proviso, South Carolina senator John C. Calhoun introduced his own resolutions that argued Congress had no right to bar slavery from any territory. Calhoun reasoned that since territories belong to all the states, both slave and free states had an equal claim on them. In a reversal of the voting on the Wilmot Proviso, the Senate passed Calhouns resolutions while the House defeated them. Northerners in Congress knew well that Calhouns resolutions were but a small step from more-serious proslavery legislation: a demand that Congress guarantee the right to bring slaves into territories and enact federally backed slave codes there.

An Ominous Vote. The votes on the Wilmot Proviso and the Calhoun resolutions marked the beginning of an ominous new chapter in the fight over the future of slavery. Division over the slavery issue had become sectional. By the late 1840s it was far from clear that the Second Party System could handle the most explosive issue of the day.

American Victory. Mexico had a larger regular army than the United States, but that turned out to be their only advantage. The better-equipped and better-armed Americans won every battle in the eighteen-month war. While Gen. Stephen Watts Kearney and Capt. John C. Frémont occupied New Mexico and California, Gen. Zachary Taylor captured city after city in northern Mexico. Finally, Gen. Winfield Scott landed an invasion force at Vera Cruz and marched his army to Mexico City. After fierce hand-to-hand combat in the Battles of Chapultepec, Molino del Rey, and Contreras, Scotts army captured the capital. The war was over.

The Wilmot Proviso, 1846

This single paragraph, attached to an appropriations bill at the beginning of the war with Mexico, framed the tense national debate over slavery until the outbreak of the Civil War. Penned by a little-known Pennsylvania congressman named David Wilmot, the proviso united Northern Whigs and Democrats opposed to slaverys expansion in the West. Although it never became law, the Wilmot Proviso provided an ominous sign that the two-party system would not be able to contain the explosive issue of slavery expansion.

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.

Manifest Destiny. Back in the United States, American expansionism was at high tide. Democratic journalist John L. OSullivan wrote in 1845 that it was our manifest destiny to overspread and to possess the whole of the continent which Providence has given us for the development of the great experiment of liberty. Some Democrats spoke in favor of taking all of Mexico. Nevertheless, on the other side, many Americans, especially those from New England and those who opposed the extension of slavery, began voicing their doubts. In Washington antiwar sentiment was mostly confined to the Whig party, but even Northern Democrats had begun to worry about the future of all the Western territory that would be gained from the victory over Mexico.

Treaty of Guadelupe Hidalgo. Discussions with the United States took place even before the federal government had made peace with Mexico. President Polk had ordered Nicholas P. Trist, chief clerk of the state department, to accompany the American armies into Mexico City and to offer $15 million for the disputed territory in Texas, California, and New Mexico. On 2 February 1848 the Treaty of Guadelupe Hidalgo was passed by the Senate 38-14, with opposition split between Democrats who wanted more territory and Whigs who opposed any expansion at all. In the end the United States gained territory that eventually became the states of California, Nevada, Utah, Arizona, and parts of New Mexico, Colorado, and Wyoming.


John S. D. Eisenhower, So Far From God: The U.S. War with Mexico 18461848 (New York: Random House, 1989);

Robert W. Johannsen, To the Halls of Montezumas: The Mexican War in the American Imagination (New York: Oxford University Press, 1985).