What Was the Significance of Manifest Destiny? Entry 7

Democrat James K. Polk (1845–1849) was the country’s 11th president, succeeding John Tyler in the White House. Polk had been a strong ally of Andrew Jackson and was a former Speaker of the House of Representatives and Governor of Tennessee. Polk’s presidency was marked by the dramatic expansion of U.S. territory and the rise of the idea known as Manifest Destiny, a term coined in 1845.

Proponents of Manifest Destiny believed that the United States had a God-given right, and perhaps even a duty, to expand across North America. They argued that American political, social, and economic institutions should spread across a much larger territory. Among these values was the belief in free enterprise and economic opportunity. This philosophy played an important role in shaping Polk’s approach to territorial expansion.

In 1846, a settlement was reached with Great Britain known as the Oregon Treaty. The treaty established the boundary between the United States and British North America west of the Rocky Mountains at the 49th parallel, with the exception of Vancouver Island, which remained under British control. The agreement ended a long-standing territorial dispute that had existed between the United States and Britain since the early nineteenth century. The United States secured the territory that would eventually become the states of Oregon, Washington, and parts of Idaho and Montana. The 49th parallel would eventually become a significant portion of the international border between the United States and Canada.

In 1845, the Republic of Texas was formally annexed by the United States, becoming the Union’s 28th state. Texas had earlier rebelled against the centralist Mexican government in 1835–1836. Following a brutal struggle that included the famous Battle of the Alamo, Texan forces achieved a decisive victory over the Mexican army at the Battle of San Jacinto in April 1836. Texas subsequently declared independence from Mexico and established the Republic of Texas. Although Mexico never formally recognized Texan independence, the United States eventually annexed Texas during Polk’s presidency. Sam Houston served as the first and third president of the Republic of Texas.

Relations with Mexico subsequently deteriorated, eventually resulting in the Mexican-American War (1846–1848). The United States emerged victorious, and under the Treaty of Guadalupe Hidalgo, Mexico ceded a vast amount of territory to the United States. This territory, known collectively as the Mexican Cession, eventually became all or parts of the modern states of California, Nevada, Utah, Arizona, New Mexico, and Colorado. The treaty also confirmed the Rio Grande as the boundary between Texas and Mexico. In return, the United States agreed to pay Mexico $15 million and assume certain financial claims made by American citizens against Mexico.

The war itself was a significant demonstration of American military power. U.S. forces invaded Mexico from several directions, and General Winfield Scott led an American campaign that captured Mexico City in September 1847. The American victory greatly expanded U.S. territory but came at a significant human and political cost.

Far from being an uncomplicated victory for the United States, the newly acquired territory created considerable domestic turmoil. The expansion of the country brought the increasingly divisive question of slavery to the forefront: would slavery be permitted to expand into the new territories? This issue intensified sectional tensions between the North and South and would contribute significantly to the political crises that eventually led to the American Civil War.

From a historical perspective, Polk is often regarded as one of the more effective presidents in achieving his stated objectives. During his single term, the United States expanded dramatically, fulfilling many of the territorial goals associated with Manifest Destiny. His administration also largely avoided the personal scandals and controversies that had damaged the reputations of some earlier presidents. Polk had promised that he would serve only one term, and he kept that pledge.

Polk was succeeded by Zachary Taylor, a military hero of the Mexican-American War. Taylor was not Polk’s preferred successor; Polk supported Lewis Cass, the Democratic presidential nominee in 1848. After leaving office, Polk retired to Tennessee. His health deteriorated rapidly, and he died in June 1849, only a few months after leaving the presidency.