Which territory was established as a result of a compromise with Britain during Polk's presidency?

The correct answer is Oregon. During President James K. Polk's administration, the United States negotiated with Britain over the Oregon Territory, which was claimed jointly by both nations. The issue at hand was the northern boundary of this territory, with the Americans advocating for "54°40' or Fight," referring to the latitude line they wanted as the northern border. However, Polk sought to avoid conflict and ultimately reached a compromise with Britain in 1846, leading to the Oregon Treaty. This treaty established the boundary at the 49th parallel, thereby defining the border between the U.S. and British North America, which is now Canada. This expansion was significant during Polk’s presidency, as it aligned with the belief in Manifest Destiny, the 19th-century doctrine that the U.S. was destined to expand across the North American continent.