#15: James W. Polk (1845-1849)

During his presidency, James K. Polk oversaw a massive territorial expansion, adding over 800,000 square miles to the United States and stretching its borders to the Pacific Ocean. His achievements in just one term were so substantial that he chose not to run for a second term, a rare decision in presidential history.

He successfully negotiated the Oregon Treaty with Britain, securing the Oregon Territory for the United States. Polk initiated the Mexican-American War, resulting in significant territorial gains, including California and New Mexico. His administration also oversaw the annexation of Texas, fulfilling Manifest Destiny and expanding the nation’s borders to the Pacific Ocean.