There were multiple reasons for the Mexican War. One immediate cause was the American annexation of Texas; the Mexican government regarded this a declaration of war, and removed the Mexican minister from Washington. Another cause was American claims against Mexico arising from the Mexican revolutions.
Following Mexico's independence from Spain, American and European cartographers fixed the Texas border at the Neuces River. Prior to Texas's independence, the Neuces River was recognized as the northern boundary of Mexico. Spain had fixed the Neuces as a border in 1816, and the United States ratified it in the 1819 treaty by which the United States had purchased Florida and renounced claims to Texas.
Throughout the 1820s, Americans settled in the vast territory of Texas, often with land grants from the Mexican government. Their numbers soon alarmed the authorities, however, who prohibited further immigration in 1830. In 1834 General Antonio Lopez de Santa Anna established a dictatorship in Mexico, and the following year Texans revolted when the new government abolished slavery.
Santa Anna defeated the American rebels at the celebrated siege of the Alamo in early 1836. On 21 April 1836 General Sam Houston with some 1,000 Texans under his command annihilated the 1,400-man army of Santa Anna. The Battle of San Jacinto lasted 18 minutes, and won Texas its independence from Mexico. When Texas declared its independence, it claimed as its territory an additional 150 miles of land, to the Rio Grande River. For almost a decade, Texas remained an independent republic.
At first, the American government strove to preserve peace with the goal to purchase New Mexico and California. The Jackson and Van Buren administrations feared both diplomatic trouble and the political consequences of admission of a new slave state; they therefore did not press the issue. The frontrunners in the 1844 presidential nominations, Democrat Martin Van Buren and Whig Henry Clay, announced they were against immediate annexation of Texas. In response, Southern democrats managed to block Van Buren's nomination, allowing dark horse James K. Polk to come to the forefront. He campaigned for the acquisition of both Texas and Oregon. Clay, seeing the popularity of Polk's stand, began hedging on the question of annexation, thus causing a defection of anti-slavery Whigs from the party, a defection which probably cost him the election.
After Texas gained its independence from Mexico, its voters overwhelmingly supported annexation into the United States. Although Mexico broke relations with the United States over the issue of Texas statehood, the most contentious issue was the new state's border: Texas claimed the Rio Grande River; Mexico argued that the border stood far to the north along the Nueces River. Meanwhile, settlers were flooding into the Mexican territories of New Mexico and California at a time when many Americans claimed that the United States had a "manifest destiny" to expand westward to the Pacific Ocean.
On 01 March 1845 Congress employed its power to admit new states, and annexed Texas by a majority vote. On the fourth of March 1845 Polk was duly inaugurated. The annexation of Texas brought into the Union all or parts of Colorado, Kansas, New Mexico, Oklahoma, and Wyoming. The admission of Texas into the Union helped to speed the disintegration of the national political parties. Many Van Buren Democrats, convinced that southerners had trampled over their rights, left the party for the Free-Soil or Republican parties. Political ideologies and political parties were thus becoming sectional, making the Civil War almost unavoidable. The United States also adopted Texas's position and claimed the Rio Grande as the border, helping to provoke war with Mexico.
The "Army of Observation" commanded bv General Zachary Taylor was deployed to Corpus Christi, at the mouth of the Nueces River, to protect newly annexed Texas in the summer of 1845. The force consisted of 5 regiments of infantry, 1 regiment of dragoons, and 16 companies of artillery.
Mexico broke diplomatic relations with the United States and refused to recognize either the Texas annexation or the Rio Grande border. President James Polk sent a special envoy, John L. Slidell, to propose cancellation of Mexico's debt to United States citizens who had incurred damages during the Mexican Revolution, provided Mexico would formally recognize the Rio Grande boundary. Slidell was also authorized to offer the Mexican government up to $30 million for California and New Mexico. At that time, New Mexico embraced much of what is now the southwestern United States, not just the present state of New Mexico.
Between Slidell's arrival on December 6, 1845, and his departure in March 1846, the regime of President Jose Herrara was overthrown and a fervently nationalistic government under General Mariano Paredes seized power. Neither leader would speak to Slidell. When Paredes publicly reaffirmed Mexico's claim to all of Texas, Slidell left in a temper, convinced that Mexico should be "chastised."
The agent for chastisement was already in place. In mid-January 1846, more than 3,500 troops commanded bv General Taylor moved south under President Polk's order from Corpus Christi to a location on the north bank of the Rio Grande. Advancing on March 8 to Point Isabel, the US troops found that the settlement had been burned by fleeing Mexicans. By March 28, the troops were near the mouth of the Rio Grande across from the Mexican town of Matamoros. The Rio Grande formed part of the border between the United States and Mexico.
Polk claimed the move was a defensive measure, and expansionists and Democratic newspapers in the United States applauded his action. Whig newspapers said that the movement was an invasion of Mexico rather than a defense of Texas. General Taylor sent one of his officers across the river to meet with Mexican officials. The Mexicans protested the movement of the American troops to the Rio Grande. They said the area was Mexican territory. The movement of American troops there, they said, was an act of war. For almost a month, the Americans and the Mexicans kept their positions. While newspapers in Mexico called for war, General Pedro de Ampudia warned, "If you insist in remaining upon the soil of the department of Tamaulipas, it will clearly result that arms, and arms alone, must decide the question."
General Ampudia's prediction came true on 25 April 1846, when General Taylor received word that a large Mexican force had crossed the border a few kilometers up the river. A small force of American soldiers went to investigate. The Mexican cavalry attacked the mounted American patrol, killing five, wounding eleven, and capturing forty-seven. General Taylor quickly sent a message to President Polk in Washington. It said war had begun.
President Polk sent his war message to Congress on May 11 asserting, "Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon America's soil." He asked congress to give him everything he needed to win the war and bring peace to the area. On May 13, Congress declared war, with a vote of 40-2 in the Senate and 174-14 in the House. President Polk signed the war bill. Later, Polk wrote: "we had not gone to war for conquest. But it was clear that in making peace we would, if possible, get California and other parts of Mexico."
A few members of congress did not want to declare war against Mexico. They believed the United States was responsible for the situation along the Rio Grande. Ohio Senator Tom Corwin accused Polk of involving the United States in a war of aggression. Senator John C. Calhoun of South Carolina abstained from voting, correctly foreseeing that the war would aggravate sectional strife. A freshman Whig Congressman from Illinois, Abraham Lincoln, questioned whether the "spot" where blood had been shed was really US soil. Other citizens shared their legislators' concern, particularly those in the Northeast who saw the war as a ploy to extend slavery. The most celebrated was Henry David Thoreau, who refused to pay his $1 Massachusetts poll tax because he believed the war an immoral advancement of slavery.
Many Americans opposed what they called "Mister Polk's War." Whig Party members and abolitionists in the North believed that slave-owners and Southerners in Polk's administration had planned the war. They believed the South wanted to win Mexican territory for the purpose of spreading and strengthening slavery. President Polk was troubled by this opposition. But he did not think the war would last long. He thought the US could quickly force Mexico to sell him the territory he wanted.
Polk secretly sent a representative to former Mexican dictator Santa Ana, who was living in exile in Cuba. Polk's representative said the United States wanted to buy California and some other Mexican territory. Santa Ana said he would agree to the sale, if the united states would help him return to power. President Polk ordered the US Navy to let Santa Ana return to Mexico. American ships that blocked the port of Vera Cruz permitted the Mexican dictator to land there. Once Santa Ana returned, he failed to honor his promises to Polk. He refused to end the war and sell California. Instead, Santa Ana organized an army to fight the United States.
The American Army that undertook the task of subduing Mexico was inconceivably small by modern standards. When the fighting started in May 1846, the regular Army had 6,562 soldiers, including 637 officers and 5,925 enlisted personnel. More than one-half of this strength (3,922 men organized in three brigades) was assembled in Texas under Taylor (who later was elected President), the largest force assembled by the United States since the War of 1812. During the course of the war, 1,016 officers and 35,009 enlisted soldiers joined the regular Army, so the total of regular troops engaged was 42,587. Another 73,532 men served in volunteer units, though not all of them reached the theaters of operations.
The initial clashes, at Palo Alto and Resaca de la Palma (near present-day Brownsville, Texas) in May 1846, were decisive American victories that threw the Mexican force back across the Rio Grande. Those battles determined that the war would be fought on Mexican soil, with the Mexican Army almost always on the defensive.
Denied the right to own land or hold office, on 14 June 1846 a band of American settlers in California arrested the Mexican govenor, and declared California an independent republic. The newly independent California Republic survived only 25 days. On 07 July 1846, an American naval vessel captured the Mexican capital at Monterey and claimed all of California for the United States.
General Taylor moved against the Mexicans. In September 1846 he crossed the Rio Grande river and marched toward Monterrey, the major trading and transportation center of northeast Mexico. The battle for Monterrey lasted three days, and the Mexicans surrendered. After capturing the city, Taylor negotiated an armistice with his opponent. Taylor needed a pause to replenish his ammunition stocks. However, the armistice was rejected by his superiors in Washington, and as soon as the slow communications of the day permitted, Taylor received orders to end the armistice and resume offensive operations. Taylor's victory at Buena Vista on 22 and 23 February 1847 was the first major battle in history in which both sides were armed for the most part with percussion weapons rather than flintlocks.
By October 1846, President Polk had decided to change strategy, holding Taylor on the defensive in the north and concentrating offensive efforts on seizing Vera Cruz and then moving inland to assault the capital, Mexico City. General Taylor was ordered to send most of his forces back to the coast. They were to join other American forces for the invasion of Vera Cruz, which would make marching to Mexico City easy. While this was happening, Santa Ana was moving his army north. In four months, he had built an army of 25,000 men. When general Taylor learned that Santa Ana was preparing to attack, he left Vera Cruz. He moved his forces into a position to fight Santa Ana, who sent a representative to meet with General Taylor. The representative said the American force had one hour to surrender. Taylor's answer was short: "tell Santa Ana to go to hell." the battle between the American and Mexican forces lasted two days. Losses were heavy on both sides. On the night of 29 March 1847, Santa Ana's army withdrew from the battlefield. Taylor had won another victory.
Other American forces were victorious, too. Commodore Robert Stockton had invaded California and had raised the American flag over the territory. Stephen Kearny had seized Santa Fe, the capital of New Mexico, without firing a shot.
The decisive campaign of the Mexican War was Winfield Scott's overland offensive designed to capture Mexico City and end Mexican resistance. In one of the great achievements in US military history, Winfield Scott's forces staged an amphibious landing at Vera Cruz that captured the port on 9 March 1847. The Mexican commander chose not to oppose the landing, so over 8,600 men were landed without a single loss in just over 4 hours. This was an unprecedented military achievement for the time. Following a brief siege, Vera Cruz surrendered on 29 March 1847.
Still, the war was not over. President Polk's "short" war already had lasted for more than a year. Polk decided to send a special diplomatic representative to Mexico. He gave the diplomat the power to negotiate a peace treaty whenever Mexico wanted to stop fighting. A ceasefire was declared, but attempts to negotiate a peace treaty failed. Santa Ana tried to use the ceasefire to prepare for more fighting.
When the war began President Polk had three strategic objectives: defend the boundary of Texas claimed by the United States, which was the Rio Grande River; seize New Mexico and California; and achieve sufficient military success in Mexico to force it to make peace on terms favoring the United States. These were ambitious goals, but they also were limited and did not envision a conquest of Mexico. Polk thought they could be achieved in 6 to 12 months by operations confined to what was then the northern portion of Mexico. When American successes in the north, including the conquest of New Mexico and California, did not lead to Mexican surrender, Polk and his advisers turned to a more ambitious campaign against the Mexican heartland aimed at capturing the capital, Mexico City.
After the capture of Vera Cruz, General Winfield Scott led the army westward via Jalapa to Pueblo, where he prepared to attack Mexico City. Scott adopted a daring strategy, cuttin his supply lines from Vera Cruz, he relied on his support trains supplemented by what could be obtained along the way. This risked isolating his army in the midst of a hostile countryside. But the gamble proved successful, and the army reached the outskirts of Mexico City on 18 August 1847.
General Scott ended the ceasefire, and began the attack on Mexico City which lasted one week. The government of Mexico surrendered on September 14, 1847, which ended the fighting. Marines participated in the capture and occupation of Mexico City and the Castle of Chapultepec, otherwise known as the "Halls of Montezuma." Following the close of the Mexican War came the first verse of the Marines' Hymn, written, according to tradition, by a Marine on duty in Mexico: "From the Halls of Montezuma, To the Shores of Tripoli."
Santa Ana stepped down as president, and Manuel de la Pena y Pena -- president of the supreme court -- became acting president. Only after the resignation of Santa Anna was the United States was able to negotiate the Treaty of Guadalupe Hildago, which was signed on 02 February 1848. The United States purchased New Mexico and California for $15 million, and paid more $3 million in damage claims that Mexico owed American citizens. In addition to Mexican recognition of the US annexation of Texas, it also recognized the Rio Grande river as the southern border of Texas.
The terms of the treaty were those set by president Polk. Yet he was not satisfied with just California and New Mexico -- he wanted even more territory. But he realized he probably would have to fight for it. And he did not think Congress would agree to extend the war. So Polk sent the peace treaty to the senate. It was approved. The Mexican congress also approved it. The war was officially over by May 1848.
The Mexican War saw the first major use of steamboats in war [though the Army made limited use of steamboats in the Second Seminole War in Florida from 1835 to 1842]. Steamboats were used to transport men and supplies down the Ohio and Mississippi Rivers to New Orleans for subsequent overseas movement. Steamboats also were used to establish a line of communication for Taylor's army along the Rio Grande when, after Resaca de la Palma, Taylor moved his army up the river in the first stage of an offensive against Monterrey.
The war proved to be a training ground for American officers who would later fight on both sides in the Civil War. Grant, Lee, Meade, Bragg, Davis, McClellan, and many others gained experience and learned lessons at Buena Vista and Cerro Gordo that later served them well at Antietam and Gettysburg. It was also a politically divisive war in which antislavery Whigs criticized the Democratic administration of James K. Polk for expansionism.
With the conclusion of the Mexican War, the United States gained a vast new territory of 1.36 million square kilometers encompassing the present-day states of Arizona, Nevada, California, Utah and parts of New Mexico, Colorado and Wyoming. But it was also a poisoned acquisition because it revived the most explosive question in American politics of the time: would the new territories be slave or free?
The United States now faced the problem of what to do with the new lands. President Polk wanted to form territorial governments in California and New Mexico. He asked Congress for immediate permission to do that. But the question of slavery delayed quick congressional action. Should the new territories be opened or closed to slavery? Southerners argued that they had the right to take slaves into the new territories. Northerners disagreed. They opposed any further spread of slavery.
The real question was this: did congress have the power to control or bar slavery in the territories? Until texas became a state, almost all national leaders seemed to accept the idea that congress did have this power. For fifty years, congress had passed resolutions and laws controlling slavery in united states territories. Northerners believed congress received the power from the constitution. Southern slave owners disagreed. They believed the power to control slavery remained with the states.
There were some who thought the earlier Missouri compromise could be used to settle the issue of slavery in California, Oregon, and New Mexico. They proposed that the line of the Missouri compromise be pushed west, all the way to the pacific coast. Territory north of the line would be free of slavery. South of the line, slavery would be permitted. Everyone agreed that governments had to be organized in the territories. But there seemed to be no way to settle the issue of slavery. Then a senator from Delaware agreed to be chairman of a special committee on the question of slavery in the new territories. The senate committee included four Whigs and four Democrats. North and South were equally represented. Within six days, the committee had agreed on a compromise bill.
Sources and Methods
- Pack Mules and Surf Boats: Logistics in the Mexican War by Robert D. Paulus Army Logistician November/December 1997
- Mexican War @ US Army Center for Military History
- INVASION YANQUI: The Mexican War, 18461848 includes a useful Essay by Frances Leonard
- The Aztec Club of 1847 descendents of commissioned officer
- The Mexican War
- Lincoln's Spot Resolutions @ National Archives and Records Administration
- James K. Polk Message on War with Mexico May 11, 1846
- Treaty of Guadalupe Hidalgo February 2, 1848
- Boundaries of the United States and the Several States
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