Winning a narrow victory as eleventh president of the United States, James K. Polk would later be credited with establishing the reputation of the United States as a continental power. During Polk's term as president, he increased the size of the United States by nearly 1.2 million square miles by securing Texas and adding the Oregon Territory and the Mexican cession lands. James K. (1795 - 1849) and Sarah (1803 - 1891) Polk