Under James Knox Polk, the United States grew by more than a million square miles, adding territory that now composes the states of Arizona, Utah, Nevada, California, Oregon, Idaho, Washington, much of New Mexico, and portions of Wyoming, Montana, and Colorado. More than any other President, Polk pursued "Manifest Destiny," a phrase coined by his fellow Jacksonian Democrat, John L. O'Sullivan, to express the conviction that Providence had foreordained the United States to spread its republican institutions across North America. He accomplished every major goal that he set for himself as President and in the process successfully waged war against Mexico, obtaining for the United States most of its present boundaries as a nation.

A man of firm personal principles, he kept his word to retire after a single term, although he easily could have won reelection. Despite Polk's accomplishments, many historians today regard him not as a great president but as one who missed opportunities. He failed to understand the depth of popular emotion over the westward expansion of the South's "peculiar institution." This failure on his part left the issue of slavery unaddressed and thus unresolved at the end of his term in 1849.

Youth and Family

Polk was born on a family farm in North Carolina. When he was ten, his family traveled by covered wagon to the frontier of Tennessee to carve a plantation out of the wilderness. The hardships of the journey damaged Polk's health for the rest of his life.

The Polk family did well financially, ultimately acquiring thousands of acres and more than fifty slaves. Polk was schooled at home and at two Presbyterian schools in Middle Tennessee. At the age of twenty, he continued his education at the University of North Carolina, graduating in 1818. He then returned home to study law under a prominent Nashville lawyer. In 1825, Polk won election to the United States House of Representatives, where he served seven terms.

Building Political Assets

Andrew Jackson enjoyed the support of Polk's father in his unsuccessful 1824 presidential campaign. When Jackson finally won the White House in 1828, Polk proved to be his closest ally in Congress. With Jackson behind him, Polk became the Speaker of the House in 1835, a position he held for four years. He so strongly supported Jackson's initiatives that his colleagues nicknamed him "Young Hickory." In 1839, he was elected governor of Tennessee.

When Polk ran for reelection in 1841, it was a bad time to be a Democrat. The country was in a severe depression, complete with bank failures and farm foreclosures, and the new Whig Party heaped blame on the party of Andrew Jackson. Polk lost the election. After a second defeat at the polls in 1843, Polk turned his attention to the family plantation.

Polk's wife, Sarah Childress, whom he married in 1824, helped him throughout his political career. A wealthy and well-educated Tennessean, she proved to be the perfect political wife of the day, entertaining and mingling easily with people—in contrast to her more reserved husband. When she settled into the life of the Polk plantation after her husband's second gubernatorial defeat, she probably had no idea that her next residence would be the White House.

Surprising Nomination and Close Election

When Democrats convened to select their presidential nominee for the election of 1844, no one expected Polk to emerge at the top of the ticket. Former President Martin Van Buren was the front-runner—but Van Buren had lost to the Whig William Henry Harrison in 1840, and many felt he was too weak a candidate. Moreover, the New Yorker had lost the support of the South due to his opposition to annexing Texas. The convention deadlocked, and prodded by Andrew Jackson, Van Buren threw his delegates behind the nation's first dark horse candidate: James Knox Polk. Opposition Whigs soon asked, "Who is James K. Polk?" In order to answer this question, Polk developed an explicit platform.

With Pennsylvania's George M. Dallas as his running mate, Polk announced his support both for the annexation of Texas and for the "reoccupation" of all of the Oregon Territory, which the United States then jointly occupied with the British between the latitudes of 42° and 54°40'. With his supporters pushing the slogan, "Fifty-Four Forty or Fight," Polk thus balanced the idea of a new slave state (Texas) with the possibility of a new free state (Oregon).

The election was vicious, with slavery and slander at its center. Both Polk and his Whig opponent, Henry Clay, owned slaves, but Clay opposed the annexation of Texas. The emergence of a third party further clouded things, and despite losing his home state of Tennessee Polk ultimately won with the thinnest margin in history.

Territory, Tariffs, and Slavery

Polk soon found himself in a crisis. After acquiring the territory containing present-day Oregon, Washington, and Idaho from the British, he turned his attention to Texas, which had been annexed by President John Tyler in his last days in office in 1845. Responding to Mexican counterclaims, Polk sent U.S. Army troops, under then-Colonel Zachary Taylor, into the disputed area on Texas's southern border. After a clash in late April 1846 between American and Mexican troops in the area, Polk requested and received a declaration of war from Congress. Within sixteen months, U.S. forces drove deep into Mexico, capturing Mexico City in September 1847. In the Treaty of Guadalupe Hidalgo, the United States imposed a Rio Grande border for Texas and paid $15 million to Mexico for the territories of California and New Mexico.

Domestically, Polk wanted to stabilize the U.S. banking system and to lower tariffs. He also found himself challenged by the Wilmot Proviso, a bill that intended to ban slavery in all territories acquired from Mexico. With fierce maneuvering on all sides, and with Polk opposed to it, the Proviso passed the House repeatedly, but the Senate never concurred. The unresolved status of slavery in the new western territories outlived disputes over banking and the tariff, becoming the most contentious issue facing the United States in the years immediately following Polk's presidency.

Polk kept his promise not to run for a second term and was succeeded in office by the hero of the Mexican War, Zachary Taylor, candidate of the opposition Whig Party and a man whom Polk despised. Less than three months later, Polk was dead, possibly of cholera contracted on a long tour of the southern states. He left most of his estate to his wife, with the request that she free their slaves upon her death. Polk left behind a country that was both larger and weaker—expanded by more than a million square miles but fatally torn over the key issue these new lands had once again brought to the fore: slavery.