American Civil War · CHAPTER 1 ·
Mexican–American War
Chapter 1 of The American Civil War, 1840–1877: “Manifest Destiny and the Mexican War”
In the 1840s the belief in Manifest Destiny drove American expansion: Texas joined the United States in 1845 and Oregon was split with Britain in 1846. When Mexico refused to sell California, President Polk sent troops into disputed land, and the Wilmot Proviso of 1846 tied the conquest to the question of slavery.
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The map above is the world of North America, July 1848 — The Cession — and the question.
Every state on the map that year: The world in 1850 · Europe in 1850.
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SHORT EXPLANATION
In the 1840s, many Americans expected expansion to strengthen their republic. An 1845 editorial gave that ambition a name: the “manifest destiny to overspread the continent.” Texas, a slaveholding republic since its break from Mexico in 1836, joined the United States in 1845 despite Mexico’s warning that annexation meant war. President James K. Polk wanted California as well. After Mexico refused to sell it, he sent troops into disputed territory. The ensuing invasion cost Mexico, already weakened by debt, coups, and Comanche raids, about half its territory.
The victory brought Americans to a question that would lead toward civil war: could slavery spread into the conquered land? In 1846 David Wilmot proposed a ban. Northern Democrats and Whigs joined against Southerners of both parties in the House, exposing a division that ran through both national parties. The map shows the land in blue-and-white hatch because its status remained undecided. In 1850 Congress admitted California as a free state and left Utah and New Mexico to decide for themselves. The compromise eased the immediate crisis while leaving Congress’s power to exclude slavery from new territory unsettled.
The full story
In the 1840s, Americans traveled west in growing numbers, and expansionists expected the government to secure the lands they entered. They called their cause Manifest Destiny: Providence, or God’s plan, had supposedly assigned the continent to the United States. This promise of national greatness carried a racial assumption that white Americans should rule. President James K. Polk made expansion a policy. Texas, a slaveholding republic since its break from Mexico in 1836, entered the Union in 1845 by a joint resolution of both houses, after the Senate rejected an annexation treaty. Britain and the United States divided Oregon at the 49th parallel, now the Canadian border; its hatching disappears from the map in June 1846.
Polk also wanted California, but Mexico refused to sell. He sent General Zachary Taylor into the strip between the Nueces River and the Rio Grande, which both countries claimed. A skirmish there in April 1846 gave Polk grounds to present the war he had chosen to risk as a war of defense. Mexicans saw an invasion intended to dismember their country, and still call it the American intervention.
Mexico faced that invasion with a government already in crisis. The republic was nearly bankrupt. Federalists seeking strong states and centralists favoring power in Mexico City struggled for control, and presidents changed more than half a dozen times in 1846–48. No leader could easily sell land and survive politically. Comanche and Kiowa raids had killed thousands in the far north, weakening a frontier the government had never fully controlled. Yet Mexicans fought hard: Santa Anna marched north to Buena Vista along the dark red arrow, and cadets defended Chapultepec, the castle guarding the capital, as Winfield Scott advanced inland from Veracruz.
The conquest brought a new problem home. Congress governed territories until they became states, much as it still governs Guam; would it permit slavery in the land taken from Mexico? In 1846 David Wilmot attached a ban to a bill granting Polk $2 million for peace negotiations. The House passed it on a sectional vote, but the Senate blocked it. Gold discovered in 1848 drew so many settlers to California that it soon sought admission as a free state. Its admission threatened the balance of slave and free states that gave the South an equal voice in the Senate.
The Compromise of 1850 dealt with the immediate dispute through several trades. California entered free; Utah and New Mexico were left to popular sovereignty, a decision by their settlers; and the South received a Fugitive Slave Act requiring Northern officials to help return people who had escaped. The hatch that remains on the 1850 map shows the question the bargain postponed.
FULL EXPLANATION
What “Manifest Destiny” meant, and who doubted it
An unsigned editorial in 1845, usually credited to John L. O’Sullivan, invoked “our manifest destiny to overspread the continent allotted by Providence.” The language suggested a national mission, but historians have found different motives within it. Reginald Horsman traced an Anglo-Saxon racial doctrine that portrayed Mexicans and Native peoples as unfit to govern their own land. Thomas Hietala found anxiety as well as confidence: fear of British power and markets glutted with unsold goods encouraged expansion. How much did slavery matter? Abolitionists saw a “Slave Power,” a supposed conspiracy of slaveholders directing Washington. Texas gives that suspicion force: John C. Calhoun defended annexation in 1844 as protection for slavery. Polk’s interest in California, by contrast, centered on harbors and trade. The war also had prominent opponents. Lincoln’s “spot resolutions” of 1847 challenged Polk’s account of its beginning, and Grant later called it “one of the most unjust ever waged by a stronger against a weaker nation.” Racial thinking could restrain expansion as well as encourage it: the 1848 movement to annex all Mexico faltered partly because Americans were unwilling to absorb millions of Mexicans.
Mexico’s war: raids, coups and a divided state
The United States invaded a country whose northern frontier had already suffered years of violence. Brian DeLay has shown that Comanche and Kiowa raids from the 1830s to 1847 struck ten northern Mexican states, killed thousands, and deepened grievances against Mexico City. The US Army encountered an exhausted region. Political divisions made negotiation as dangerous as resistance. At the turn of 1846 General Mariano Paredes overthrew President José Joaquín Herrera, partly because Herrera appeared willing to receive Polk’s envoy. Santa Anna passed through the US blockade after privately promising peace, then took command and fought. When Scott landed in March 1847, Yucatán had broken away and the capital had just endured the revolt of the polkos, militia units opposing a decree to seize church property. The human cost is uncertain because records are incomplete: perhaps 5,000 Mexican soldiers died in battle, and deaths from disease and among civilians may have brought the total to 25,000. Mexican writers in 1848 blamed American greed; Josefina Zoraida Vázquez weighs that ambition against the weakness of a state not yet consolidated. To understand why Mexico could not defend itself, we have to consider both the invasion and the divisions that preceded it.
Why 1850 was an armistice
Henry Clay tried to pass the Compromise of 1850 as an omnibus bill, a single package of laws like those Congress still uses for budgets. The Senate broke it apart on 31 July 1850. Stephen A. Douglas then secured passage of the separate measures, but separate passage mattered: Holman Hamilton’s study of the roll calls found a different coalition behind each one. Northerners supplied votes for free-state measures and Southerners for measures favoring slavery. Only a small bloc of Northern Democrats and men from border slave states supported nearly everything. No majority had endorsed the whole bargain. President Zachary Taylor’s death on 9 July also changed its prospects. He had threatened a veto; his successor, Millard Fillmore, signed every bill. David Potter called the result an armistice, a pause that settled no principle. Consider popular sovereignty: Northern and Southern Democrats could agree on the phrase while disagreeing about whether settlers could decide on slavery during the territorial stage or only at statehood. The dispute remained inside the formula meant to contain it.
Key places on the map
On this day
Why it happened
Land hunger and an ideology of destiny. The brown arrow follows the Oregon Trail, traveled by thousands in the 1840s. As settlers moved west, they looked to Washington to secure the land they entered. Expansionists gave the movement a larger meaning through Manifest Destiny: Providence had supposedly assigned the continent to the United States. Pacific ports promised trade with China, while racial ideas encouraged the belief that Mexicans and Native peoples should give way.
Polk’s determination to have California. Polk took office in 1845 determined to acquire California, whose harbors at San Francisco and San Diego offered access to the Pacific. He first sent John Slidell to Mexico City, authorized by most accounts to offer up to $25 million. Mexico refused to receive him. Polk then sent Taylor’s army to the Rio Grande, into land held by Mexico and claimed by Texas. An attempt to buy territory had given way to an armed standoff.
A Mexican state at its weakest. Mexico had little room to respond to Polk. Its treasury was empty, generals made and unmade governments, and Comanche and Kiowa raids had devastated northern states. A leader who discussed selling land risked overthrow: Paredes toppled Herrera after Herrera showed willingness to talk. Mexico was poorly placed both to deter the United States and to bargain with it.
Texas and the politics of slavery. The argument over Texas was also an argument over slavery. In 1844 Calhoun told the British minister that annexation would protect it from British abolitionism; the Senate rejected the treaty that June partly for that reason. Texas entered as a slave state by joint resolution in 1845. Northern opponents saw the “slave power,” their name for slaveholders’ supposed control of federal government, extending its reach. When war brought the prospect of still more territory, that suspicion followed it into Congress.
THE TURNING POINT
The Wilmot Proviso, 8 August 1846. David Wilmot was a first-term Pennsylvania congressman when, on the night of 8 August 1846, he added a sentence to a bill granting Polk $2 million to negotiate peace. His proviso would exclude slavery from any territory taken from Mexico. The House approved it 83 to 64: Northern Democrats and Whigs joined against Southerners of both parties. The national parties depended on cooperation across the sections, and this vote showed how slavery could break that cooperation. The Senate never passed the proviso, but the question returned in 1850, 1854, and 1860.
What it changed
Free soil becomes a party. Opposition to slavery’s expansion could unite Northerners who were not prepared to challenge slavery where it already existed. Their cause was free soil: western land reserved for free labor. In 1848 the Free Soil Party nominated former president Martin Van Buren and won about ten percent of the popular vote. Many of its leaders and its slogan, “Free Soil, Free Speech, Free Labor, and Free Men,” passed into the Republican Party in the 1850s. Lincoln’s 1860 platform carried forward the principle of the Wilmot Proviso.
The Fugitive Slave Act radicalizes the North. The Fugitive Slave Act was meant to reassure the South, but its enforcement brought the power of slavery into Northern towns. Accused fugitives received no jury trial, and federal commissioners were paid $10 for sending a person south and $5 for setting one free. Crowds in Boston and elsewhere tried to rescue captured people. Harriet Beecher Stowe wrote Uncle Tom’s Cabin in response. A concession to slaveholders became a source of Northern resistance.
Popular sovereignty carries the quarrel to Kansas. Why not let settlers decide whether to permit slavery? Popular sovereignty offered that democratic answer, and Stephen Douglas applied it to Kansas and Nebraska in 1854. His legislation repealed the Missouri Compromise’s 1820 line at 36°30′ between slave and free territory. On the continental map, hatching spreads across the plains in June 1854. The decision itself became the object of fighting: Kansas turned into a small civil war, carrying the quarrel from Congress to a frontier where no one could arbitrate it.
Mexico trains the generals of 1861. Grant, Lee, Jackson, Longstreet, McClellan, and Jefferson Davis served in Mexico before becoming commanders in 1861. They learned their trade in the same war and knew one another’s habits. Grant later wrote that the Southern rebellion “was largely the outgrowth of the Mexican war,” and saw the Civil War as punishment for that conquest. The earlier war had trained men who would fight over the question its victory reopened.
DISCUSSION QUESTION — Was the Mexican War a war for slavery?
Texas supplies a strong reason to connect the war with slavery. It entered the Union as a slave state after Calhoun had defended annexation as protection for slavery, and many Southerners supported the war. Yet support and opposition did not divide neatly by section: Northern Democrats backed the war, while Southern Whigs opposed it partly because they feared the effect of new territory on the Union. Polk’s own aims centered on California’s harbors and trade, and few planters expected cotton to grow in much of the Mexican Cession, the land Mexico gave up in 1848. The distinction between why the war began and what followed from it matters. It was fought chiefly for land and ports. Once that land had been won, Congress had to confront the expansion of slavery. Slavery shaped the consequences of conquest even where it had not determined the decision to fight.
An interesting fact
Nicholas Trist signed the peace treaty after Polk had ordered him home. The recall was issued in October 1847 and reached Trist in mid-November. He stayed, explaining in a letter of some sixty-five pages that Mexico’s moderate government might fall before a replacement could arrive. On 2 February 1848 he signed at Guadalupe Hidalgo. Polk was furious, but the treaty gave him nearly everything he wanted, so he sent it to the Senate. Trist was dismissed and remained unpaid until 1871, when Congress, pressed by Senator Charles Sumner, paid his salary and expenses.
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