From whom did the United States get the Oregon Territory?

The original Oregon Territory was far more than the area that comprises the U.S. State of Oregon today.  In the first half of the 1800s, Oregon Territory included what is today Oregon, Washington, and a large part of British Columbia.  The original countries that laid claim to this large area of territory were Russia, the United States, England, and Spain.  Due to the Onís-Adams Treaty, new borders were drawn by the United States and Spain according to the Louisiana Purchase.  During this process, "the United States recognized Spanish sovereignty over Texas" in return for the surrender of the latter's Pacific Northwest territories.  Due to increased migration of Americans via the Oregon Trail, defined borders of which country owned what land became more important.  Treaties and discussions between Britain and the U.S. resolved the border issue.  President Monroe challenged Russia's claims to the territory.