James K. Polk, a relatively obscure former Tennessee governor, defeated Henry Clay in the U.S. presidential election on a platform of aggressive territorial expansion, including the annexation of Texas and claims to Oregon. His narrow victory, decided by fewer than 40,000 popular votes, propelled the United States toward war with Mexico and the acquisition of vast western territories, fulfilling — and fueling — the era's doctrine of Manifest Destiny.
Polk was such an unlikely nominee that newspapers coined the phrase 'Who is James K. Polk?' as a taunt from Whig opponents. He had been out of elected office for years, having lost bids for Tennessee governor, when the Democratic convention deadlocked and turned to him as a compromise candidate who firmly backed the annexation of Texas — a position his rivals hedged on.
The election hinged on a handful of states, New York above all, where a third-party abolitionist candidate siphoned enough votes from Henry Clay to hand Polk the state and the presidency. Polk had promised to serve only one term, and he used it with startling efficiency: he oversaw the annexation of Texas, negotiated the Oregon boundary with Britain, and provoked a war with Mexico that, by its end in 1848, had added California, New Mexico, and the entire Southwest to the United States.
By the time he left office in 1849, exhausted and in failing health, the continental shape of the modern United States was largely set. Polk died just three months after his term ended, having achieved nearly every goal he set — at a cost historians still weigh against the war's toll on Mexico and the expansion of slavery's reach.
Key people: James K. Polk, Henry Clay