The rush of settlers beyond the nation's borders in the 1830s and 1840s inspired politicians and propagandists to call for the annexation of those areas occupied by the migrants.  Some went further and claimed that it was the "Manifest Destiny" of the United State to expand until it had absorbed all of North America, including Canada and Mexico.  Such ambitions, and the policies they inspired, led to a major diplomatic confrontation between Great Britain and eventually, to war with Mexico.

       President John Tyler initiated the politics of Manifest Destiny.  Tyler had succeeded to the presidency upon the death of William Henry Harrison in 1941.  Tyler, a states' right Virginian and Whig, was profoundly out of sympathy with his own party, and soon broke with the Whigs in Congress.  Although he lacked a strong base in either party, Tyler hoped to be elected president in his own right in 1844.  To that end, he needed a new issue around which he could rally a new following that would cross existing party lines.  So in 1843, Tyler put the full weight of his administration behind the annexation of Texas.  He thought this would be a popular move, especially with the South, where it would feed the appetite for additional slave states.  To achieve his objectives, Tyler enlisted the aid of John C. Calhoun.  Calhoun saw the annexation of Texas as a way of uniting the South and taking the offensive against the abolitionists in the North.  Success or failure on this issue would constitute a decisive test of whether or not the North was willing to give the southern states their fair share of national power and accurate assurances that their way of life would remain protected.  In short, if antislavery sentiment blocked annexation of Texas, then at least Southerners would know where they stood and could begin to reexamine their relationship to the Union.

       Part of the overall strategy for winning annexation was to tie up the annexation with old fears of British domination.  According to American reports, the British were trying to build an alliance with an independent Texas by giving them a loan in return for the abolition of slavery in the new Republic.  The story is probably false, but it gave the pro-annexation forces grist for their mill.

       The U. S. Secretary of State, Abel Upsher, was a pro slavery Virginian and a protege of Calhoun.  Upsher began negotiating a treaty of annexation, but was killed in a riding accident before he could finish.  Calhoun replaced him in office, however, and the negotiations were brought to a successful conclusion.  When the treaty was brought before the Senate in 1944, Calhoun denounced the British for attempting to subvert the institution of slavery and accused them of trying to use Texas as a base for abolitionist operations.  Because of the danger of British interference, said Calhoun, it was necessary that Texas be annexed right away.

       This attempt by Calhoun to link the Texas issue with the threats against slavery aroused northern antislavery Whigs to denounce the whole scheme as a pro slavery plot to advance the interest of one section of the nation against the other.  The Senate subsequently rejected the treaty in June 1844.  Tyler then tried to bring Texas into the Union by alternate means--a joint resolution of both Houses of Congress, but Congress adjourned before this could be pulled off.  And so the entire question hung in the balance in anticipation of the election of 1844.

       Tyler's actions had made Texas the central issue of the 1844 campaign.  But party lines held firm, and Tyler himself was unable to capitalize on the issue.  He was unable to attract enough support from either party and so was forced to withdraw from the race.  The Democrats hoped to nominate Van Buren, but a delay in the opening of the convention allowed the Texas issue to once again come to the fore, and Van Buren was forced to take a stand on it.  He maintained the view that annexation of Texas would bring war with Mexico and sectional strife, and eventually destroy the unity of the Democratic party.  In an effort to keep the issue out of the campaign, though, Van Buren struck a deal with Whig leader Henry Clay:  both men would oppose the annexation of Texas, and so both parties would nullify the issue. 

       However, it was too late for Van Buren, who had already angered southerners, who blocked his nomination.  The Democrats nominated James K. Polk of Tennessee instead.  Polk had been a protege of Andrew Jackson, Speaker of the House, and governor of Tennessee.  He was an avowed expansionist and ran on a platform advocating annexation of Texas and asserting American claims to all of Oregon.  He thus identified himself with the forces of Manifest Destiny, and attracted support from all parts of the country. 

        Polk won the election by a narrow margin.  The narrowness of the victory meant that the Democrats had something less than a clear mandate over its expansionist policies, but this did not prevent them from claiming that the people had backed them in their campaign to extend the borders of the United States.  After the election, Congress reconvened to consider annexation.  The mood had changed as a result of Polk's victory, and as a result, annexation was approved a few days before Polk took office.

       Matters were still open in the question of Oregon.  In 1845 and 1846, the U. S. nearly went to war with Britain over the issue.  Pro-expansionists adopted the cry "Fifty-four forty or fight!" (referring to the southern border of Alaska). Privately, though, Polk was considering acceptance of the British offer to make the 49th parallel the border.  So in 1845, Polk authorized his Secretary of State, James Buchanan, to respond to British terms by agreeing to the offer.  However, this did not solve other questions, such as British demands for Vancouver Island and free navigation of the Columbia River.  So the British ultimately rejected the offer and infuriated Polk.  Polk withdrew the offer and refused to submit the matter to international arbitration.  Instead, he called a joint session of Congress to terminate the agreement of joint occupation between Britain and the U. S.  Congress complied in April 1846, and Polk submitted the required one year's notice to Great Britain.

       Since the U. S. had ended their agreement, the implication was that the U. S. would attempt to extend its jurisdiction to the 54th parallel.  In order to avert war, the British sent a diplomatic delegation to Washington, while at the same time, sending more warships to the Pacific Northwest just in case.  The new British proposal accepted the 49th parallel as a southern boundary, except for where it dipped south of Vancouver island.  It also gave the British navigation rights on the Columbia River.  Polk refused to accept or reject it, but sent it to the Senate for advice.  The Senate recommended that it be accepted, and it was ratified on June 15.

       The reason that Polk accepted the same terms he had rejected before was because he now had a war on his hand with Mexico -- just as Van Buren and others had predicted.  Polk's reckless diplomacy had almost gotten American involved in two wars at the same time.  By accepting the reduced terms in Oregon, Polk angered the Manifest Destiny crowd, which wanted all of Oregon.  Still, the fact that the U. S. had gotten part of Oregon was the only bright spot for northerners who hated to see the annexation of Texas as a slave state.  They became convinced that Polk was acting only in the interests if his native section and not in the best interests of the country.

      In early 1845, when Congress voted to annex Texas, Mexico expelled the American ambassador and cut diplomatic relations. But it did not declare war.

      President Polk told his commanders to prepare for the possibility of war. He ordered American naval vessels to position themselves outside Mexican ports. And he dispatched American forces in the Southwest to Corpus Christi, Texas.

      Peaceful settlement of the two countries' differences still seemed possible. In the fall of 1845, the President offered $5 million if Mexico agreed to recognize the Rio Grande River as the southwestern boundary of Texas. Earlier, the Spanish government had defined the Texas boundary as the Nueces River, 130 miles north and east of the Rio Grande. No Americans lived between the Nueces and the Rio Grande, although many Hispanics lived in the region.

      The United States also offered up to $5 million for the province of New Mexico--which included Nevada and Utah and parts of four other states - and up to $25 million for California. Polk was anxious to acquire California because in mid-October 1845, he had been led to believe that Mexico had agreed to cede California to Britain as payment for debts. Polk also dispatched a young Marine Corps lieutenant, Archibald H. Gillespie, to California, apparently to foment revolt against Mexican authority.

      The Mexican government, already incensed over the annexation of Texas, refused to accept an American envoy. The failure of the negotiations led Polk to order Brigadier General Zachary Taylor to march 3,000 troops southwest from Corpus Christi, Texas, to "defend the Rio Grande" river. Late in March of 1846, Taylor and his men set up camp along the Rio Grande, directly across from the Mexican city of Matamoros, on a stretch of land claimed by both Mexico and the United States.

      On April 25, 1846, a Mexican cavalry force crossed the Rio Grande and clashed with a small American squadron, forcing the Americans to surrender after the loss of several lives. On May 11, after he received word of the border clash, Polk asked Congress to acknowledge that a state of war already existed "by the act of Mexico herself...notwithstanding all our efforts to avoid it." "Mexico," the President announced, "has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil." Congress responded with a declaration of war.

      The Mexican War was extremely controversial. Its supporters blamed Mexico for the hostilities because it had severed relations with the United States, threatened war, refused to receive an American emissary or to pay the damage claims of American citizens. In addition, Mexico had "invaded our territory and shed American blood on American soil." Opponents denounced the war as an immoral land grab by an expansionistic power against a weak neighbor that had been independent barely two decades.

     During the first few weeks following the declaration of war a frenzy of prowar hysteria swept the country. Two hundred thousand men responded to a call for 50,000 volunteers In New York, placards bore the slogan "Mexico or Death." Many newspapers, especially in the North, declared that the war would benefit the Mexican people by bringing them the blessings of democracy and liberty. The Boston Times said that an American victory "must necessarily be a great blessing," because it would bring "peace into a land where the sword has always been the sole arbiter between factions" and would introduce "the reign of law where license has existed for a generation."

      But from the war's very beginning, a small but highly visible group of intellectuals, clergymen, pacifists, abolitionists, and Whig and Democratic politicians denounced the war as brutal aggression against a "poor, feeble, distracted country."

      Literary and reform circles were particularly vocal in their opposition to the war. Congregationalist minister Theodore Parker declared that if the "war be right then Christianity is wrong, a falsehood, a lie." Abolitionist William Lloyd Garrison's militant newspaper, The Liberator, expressed open support for the Mexican people: "Every lover of Freedom and humanity throughout the world must wish them the most triumphant success."

      Most Whigs supported the war--in part, because two of the leading American generals, Zachary Taylor and Winfield Scott, were Whigs, and in part because they remembered that opposition to the War of 1812 had destroyed the Federalist party. But many prominent Whigs, from the South as well as the North, openly expressed opposition. Thomas Corwin of Ohio denounced the war as merely the latest example of American injustice to Mexico: "If I were a Mexican I would tell you, `Have you not room enough in your own country to bury your dead.' " Henry Clay declared, "This is no war of defense, but one of unnecessary and offensive aggression."

      A freshman Congressman from Illinois named Abraham Lincoln lashed out against the war, calling it immoral, pro slavery, and a threat to the nation's republican values. In Congress, he proposed the so-called "Spot Resolution," demanding that President Polk identify the precise spot on which Mexicans had "shed American blood on American soil." One of Lincoln's constituents branded him "the Benedict Arnold of our district," and he was denied renomination by his own party.

      As newspapers informed their readers about the hardships of life on the front, public enthusiasm for the war began to fade. The war did not turn out to be the romantic exploit that Americans envisioned. Troops complained that their food was "green with slime" and "acted as an instantaneous emetic." Diarrhea, amoebic dysentery, measles, and yellow fever ravaged American soldiers. Seven times as many Americans died of disease and exposure as died of battlefield injuries. Of the 90,000 Americans who served in the war, only 1,721 died in action. Another 11,155 died from disease and exposure to the elements.

      Public support for the war was further eroded by reports of brutality against Mexican civilians. Newspaper reporters claimed that the chapparal was "strewn with the skeletons of Mexicans sacrificed" by American troops.  After one of their members was murdered, the Arkansas volunteer cavalry surrounded a group of Mexican peasants and began an "indiscriminate and bloody massacre of the poor creatures." A young lieutenant named George G. Meade reported that volunteers in Matamoros robbed the citizens, stole their cattle, and killed innocent civilians "for no other object than their own amusement." If only a tenth of the horror stories were true, General Winfield Scott wrote, it was enough "to make Heaven weep, & every American of Christian morals blush for his country."

      Dissent even made its way to the battlefield. A group of enlisted Irish-Catholic Americans, shocked by the desecration of Catholic churches, deserted to the Mexican side, formed the San Patricio Battalion, and fought against the American army. At Churubusco, 65 members of the battalion (which also consisted of foreign nationals resident in Mexico) were captured. Fifty were executed and 11 others were punished with fifty lashes apiece and the letter D (for deserter) branded on their cheeks.

      A young essayist and poet named Henry David Thoreau staged the best known act of protest against the Mexican war. On July 23, 1846, the constable of Concord, Massachusetts, arrested the Transcendentalist poet for failure to pay the state poll tax (a head tax on male citizens between the ages of 21 and 70). The constable actually offered to pay the tax if Thoreau was short of money, but Thoreau insisted that he refused to pay on principle, as a protest against his country's involvement in the Mexican War. The constable then placed Thoreau in the local jail. Thoreau spent only a single night in jail because his tax was paid, much to his disgust, by one of his relatives.

      In response to his arrest Thoreau wrote an essay that became a source of inspiration for Leo Tolstoy, Mahatma Gandhi, and Martin Luther King, Jr.  Thoreau entitled his essay "Civil Disobedience."   In it he declared that if all citizens who opposed the Mexican War followed his example and went to jail for their beliefs, the government could be forced to end the conflict. It was the duty of every individual to protest a government policy, even though it had been adopted with majority consent, when it conflicted with moral law. "Any man more right than his neighbor," he wrote, "constitutes a majority of one."

      So how should an individual protest a moral wrong? Here Thoreau was at his most creative.  He described a type of disobedience that disrupted the everyday workings of society and dramatized the moral issues at stake, without resorting to violence.  Individual acts of protest, he argued, would awaken the conscience of those people whose consciences could still be stirred.

       Although Mexico had recognized Texan independence in 1845, they rejected the Texans' dubious claim to the disputed territory between the Nueces and the Rio Grande.  When the U. S. annexed Texas and assumed its claim to the disputed area, Mexico broke off diplomatic relations and prepared for war.  The United States soon sent forces under General Zachary Taylor, and the war was on.

       The war lasted much longer than expected because the Mexicans refused to make peace despite a succession of military defeats.  Americans forces under Gen. Taylor's forces defeated the larger Mexican army at Buena Vista on Feb. 23, 1847, and was hailed as a national hero.  Yet another expedition under Gen. Stephen Kearny captured Sante Fe and proclaimed the annexation of New Mexico, then set out for California.  Before he could arrive, the American settlers revolted against Mexico and declared their independence as the "Bear Flag Republic."  Mexican opposition in California was finally finished by the end of 1847.  Finally, American forces under Gen. Winfield Scott landed at Veracruz, a crucial Mexican port city, in March of 1847, and eventually captured it, then marched onwards to Mexico City.  A force under Gen. Santa Anna blocked their way at Carro Gordo, and the two armies met there on April 17 and 18, 1847, where Scott was finally able to outflank the Mexicans and win the battle.  By August, American troops were drawn up in front of Mexico City.  After a brief armistice, which the Mexicans used to regather their forces, Gen. Scott attacked and captured the city on Sep. 14.

       Accompanying Scott was an American diplomat, Nicholas Trist, who was authorized to negotiate a peace treaty with the Mexicans.  But no Mexican leader wanted to risk the wrath of the citizenry by agreeing to Polk's terms, and in November, Polk sent orders to Trist to return to the U. S.  Radical adherents of Manifest Destiny were now clamoring to annex all of Mexico, but thankfully, in this case, Polk resisted the temptation.  Back in Mexico City, Trist had ignored Polk's orders to return, and there, on February 2, 1848, he signed the Treaty of Guadalupe Hidalgo, which gave the Americans all the concessions they'd wanted.  The Treaty ceded New Mexico and California to the U. S. for $15 million, and established the Rio Grande as the border between Texas and Mexico.  The treaty promised that the U. S. would take up the claims of American citizens against Mexico, and would allow Mexican citizens in the ceded territories to become U. S. citizens.  When the agreement reached Washington, Polk censured Trist for disobeying orders, but approved most of the treaty, which was approved by the Senate on March 10, 1848.

       As result of the Mexican War, the United States gained 500,000 square miles of territory.  The treaty enlarged the size of the nation by twenty percent, adding to its domain the present states of California. Utah, New Mexico, Nevada, and Arizona.  Later, a small strip of land on the southern edge of New Mexico and Arizona was purchased in 1853, in the Gadsden Purchase, to provide a possible land route for a transcontinental railroad that would run through a southern route instead of a northern one.

       So the Mexican War is important because the territories gained by the United States reopened the Pandora's box of slavery and the westward expansion.  But the War was also important from a military standpoint:  many of the officers who fought in this war later assumed positions of great importance on both sides during the Civil War -- Grant and Lee, Sherman, Meade, McClellan, Beauregard, Stonewall Jackson, and Jefferson Davis.  So the Mexican War, in many ways, was a prelude to the conflicts that split the nation during the decade to come.

     The story of America's conflict with Mexico tends to be overshadowed by the story of the Civil War, which began only a decade and a half later. In fact, the conflict had far-reaching consequences for the nation's future. It increased the nation's size by a third, but it also created deep political divisions that threatened the country's future.