Final answer:
James K. Polk aimed to gain access to the Pacific Ocean through compromise over the Oregon Territory with Britain, establishing the 49th parallel as the northern border, and through the acquisition of territories from Mexico, resulting in the U.S. expanding from the Atlantic to the Pacific.
Step-by-step explanation:
James K. Polk and Pacific Ocean Access
President James K. Polk was driven by the spirit of "manifest destiny" which was the belief in the divine right and duty of White Americans to expand across the continent. Polk's ambition included acquiring territories from Mexico, specifically the provinces of New Mexico and California, as well as securing the Oregon Territory. He was prepared to use force if necessary, but initially sought peaceful acquisition. To concentrate on the expansion southward, Polk compromised with the British on the Oregon issue, agreeing to the 49th parallel as the northern border, which provided access to the Pacific Ocean through Puget Sound, a strategic deepwater port. This strategic move allowed the U.S. to focus on the Mexican-American War that resulted in annexing more territory, ultimately fulfilling Polk's and the expansionists' dreams of a republic stretching from the Atlantic to the Pacific.