Place: Washington, D.C.
Following the Louisiana Purchase, the boundaries of American and Spanish Florida were disputed. Negotiations between Spain and the United States to set permanent boundaries largely stalled until Andrew Jackson's invasion of Florida during the Seminole War forced the issue. The resulting treaty, negotiated by John Quincy Adams and Don Luis de Onis was officially proclaimed on February 22, 1821. It ceded all of Florida to the United States and extended the American northwest to the Pacific coast. The United States gave up its claim on Texas and assumed $5,000,000 in claims against Spain. This largely settled America's western boundaries until the Oregon crisis and Mexican War reopened the issue in the 1840s.
Howard Jones, Crucible of Power: A History of American Foreign Relations to 1913 (Wilmington, DE: SR Books, 2002), 95-103, 137-139.