Why was the Oregon territory contested?

In the early 19th century, both the British and US has reasons to annex the Oregon area.

Before the 19th century, Spain, Russia, Britain, and the US had laid claims to large stakes in the land that is now Oregon. Disputes were common until the Adams–Onís Treaty in which Spain formally withdrew from the area. Russia followed soon after. However, the next two to three decades brought turmoil to the area and the nations desiring the land. The British had a significant naval presence in the area alongside many corporations and trading companies active in disputed lands, while the United States' Oregon Trail led nearly 700 people to the area in 1843. The dispute was not resolved until 1846 with a formal resolution and treaty.

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