WAR WITH MEXICO
The reasons for the Mexican-American War are numerous. Patriots in Mexico were outraged when Texas joined the United States, as they considered Texas still to be part of Mexico. The war served the economic interests of groups both in Mexico and the United States. However, the main reason for war was the determination of President Polk to fulfill what he perceived to be America’s mission to occupy the lands all the way to the Pacific Ocean and his willingness to use force to accomplish this aim.
Polk did much to provoke war with the Mexicans. He encouraged settlers in Mexico to occupy territory all the way to the Rio Grande River, which the Mexicans considered to be outside of the territory of Texas (Mexico considered the Nueces River, north of the Rio Grande, as the border between Texas and the rest of Mexico). Polk also wanted to buy territory from Mexico that would allow the United States to expand all the way to California. In October 1845, he offered the Mexican government $5 million for the territory between the Nueces and the Rio Grande rivers, $25 million for California, and $5 million for other Mexican territory in the West. John Slidell, the diplomat sent to Mexico City with Polk’s offer, was never even received by the Mexican government. Early in 1846 Polk sent an American force commanded by General Zachary Taylor to defend the territory between the Nueces and the Rio Grande rivers. In early April part of this force was ambushed by the Mexican army. Polk had to do little to convince the American Congress to issue a declaration of war against Mexico on May 13, 1846.
Many Whigs had hoped the conflict with Mexico could be peacefully negotiated; abolitionists feared the conflict with Mexico was little more than a Southern ruse to expand slavery in the American territories. Texas had never achieved real prosperity since its independence from Mexico, and the Mexican government was riddled with corruption. President Polk had predicted that the Mexicans would refuse American efforts to purchase western territories, and he proceeded through officials stationed there to let Americans and Mexicans living in California know that if they rose in opposition to Mexican control of the area, the American army would protect them. Not coincidentally, American naval and infantry forces arrived in California in late 1845 as a show of American force. Shortly after the American declaration of war against Mexico, settlers rose up in revolt, supported by American infantry forces commanded by John C. Fremont. On July 4, 1846, the Bear Flag Republic was officially proclaimed in the California territory.
American troops also entered into Mexico itself, easily defeating the Mexican army. Forces under Zachary Taylor were especially successful in winning battles over the Mexicans in late 1846 and early 1847. The Mexican government refused to surrender or negotiate with the Americans. President Polk then sent an American force under General Winfield Scott to Mexico to occupy Mexico City, the capital. Scott landed on Mexican territory at Veracruz on March 8, 1847, and was victorious in several battles against the Mexicans. Mexico still refused to settle for peace, and on September 13, 1847, Scott’s army entered Mexico City. Mexican partisans continued guerrilla warfare well into 1848.
Effects of the Mexican War
The Treaty of Guadalupe Hidalgo was signed on February 2, 1848, and officially ended the Mexican-American War. Many who had favored war considered the treaty too generous to the defeated Mexicans. For $15 million the United States acquired the Texas territory north of the Rio Grande, New Mexico, and California (the exact territory they had previously offered to buy). The American government also assumed all claims of Americans against the Mexican government.
The territory of the United States increased by one-third as a result of this treaty, yet the controversy over slavery in the new territories was immense. In 1846 David Wilmont, a Democratic Representative from Pennsylvania, introduced an amendment to a bill authorizing funding for the Mexican-American War that stated slavery could not exist in any territory acquired from Mexico. The Wilmont Proviso was passed by the House of Representatives four times and rejected by the Senate each time. Nevertheless, each debate concerning the bill stirred up intense sectional differences concerning slavery in the territories. Southerners such as John C. Calhoun strenuously argued that the federal government had no right to outlaw something in an American territory that was legal in a number of American states. President Polk’s compromise decision was to continue the line drawn by the Missouri Compromise out to the Pacific Ocean, with slavery allowed in territories south of the line and not allowed in territories north of the line.
To avoid being hurt by the controversies surrounding slavery, both the Democrats and the Whigs said little about it in the 1848 presidential election. Zachary Taylor ran as a Whig and was victorious, largely because of his war record in Mexico and because he made no comments whatsoever about the future of slavery in the territories. Some members of the Liberty party and defectors from the Whig and Democratic parties formed the Free-Soil party, whose main purpose was to oppose slavery in the newly acquired western territories. The Free-Soilers nominated former president Van Buren, who won 10 percent of the popular vote.