The United States needed to negotiate with Great Britain to obtain the Oregon territory.
Under the manifest destiny quest, the expansionists pressured the president Polk to request the Oregon territory. The president was on expansionist's side and was willing to start a war, if needed, to fulfill the US greed for new lands. Fortunately, the British were not looking to start a new conflict with the US and risk their profitable trades. So in 1846, the British submitted a draft treaty that extended the border between the United States and Canada along the 49th parallel.
