As president, Polk earned a reputation for being a workaholic and is remembered for his conviction that it was America’s “manifest destiny” to expand freely across the continent and spread democracy. In 1846, spurred by a desire to gain Mexican territory for the United States, Polk led the country into a controversial war with its southern neighbor. Polk insisted that Mexico had “invaded” the U.S. during an earlier skirmish between American and Mexican troops that had spilled over the ill-defined territorial boundary along the Rio Grande River. His most vocal opponent in Congress was a representative from Illinois named Abraham Lincoln.
Lincoln protested not so much expansionism itself, but Polk’s justification of the war, which he described as unconstitutional, unnecessary and expensive, calling Polk “a bewildered, confounded and miserably perplexed man.” Although the Mexican-American War was ultimately successful in territorial terms, Polk lost public support after two bloody years of conflict in which the U.S. lost 13,780 men and spent a whopping $100 million. Toward the end of 1848, Lincoln, who was beginning to make a name for himself as a persuasive orator, began coaching a Whig Party presidential candidate who would become Polk’s successor: Zachary Taylor. Ironically, Taylor had first won public recognition while serving as commanding general of the Army during the Mexican-American War.
Polk’s acquisition of 525,000 square miles of new territory caused heated debate in Congress over the question of whether the new states carved out of the territory would allow slavery. This issue would become the most divisive debate to face Congress and the nation since the American Revolution.
Polk died three months after leaving office from an intestinal disorder that his doctors claimed was aggravated by overwork.
