James K. Polk

Polk presided over significant territorial expansion: he facilitated the annexation of Texas, negotiated the Oregon Treaty with Britain setting the 49th parallel, and, after the Mexican–American War, secured California and the Southwest under the 1848 Treaty of Guadalupe Hidalgo.

On the domestic front Polk reestablished the Independent Treasury and enacted the Walker Tariff, lowering tariff rates. His accomplishments fulfilled a one-term promise, but his expansionist policies and the war with Mexico intensified sectional disputes over the extension of slavery.

Annexed Texas and settled Oregon boundary at the 49th parallel (Oregon Treaty 1846); Won the Mexican–American War and secured vast territories via the Treaty of Guadalupe Hidalgo (1848); Reestablished the Independent Treasury and implemented fiscal reforms; Enacted the Walker Tariff of 1846, lowering tariff rates; Kept a one-term pledge after completing his four main objectives