American expansionists favored setting the border at the Rio Grande, but Spain, intent on protecting its colony of Mexico from American encroachment, insisted on setting the boundary at the Sabine River. At Monroe's direction, Adams agreed to the Sabine River boundary, but he insisted that Spain cede its claims on Oregon Country.[78] Adams was deeply interested in establishing American control over the Oregon Country, partly because he believed that control of that region would spur trade with Asia. The acquisition of Spanish claims to the Pacific Northwest also allowed the Monroe administration to pair the acquisition of Florida, which was chiefly sought by Southerners, with territorial gains favored primarily by those in the North.[79] After extended negotiations, Spain and the United States agreed to the Adams–Onís Treaty, which was ratified in February 1821.[75] Adams was deeply proud of the treaty, though he privately was concerned by the potential expansion of slavery into the newly acquired territories.[80] In 1824, the Monroe administration would strengthen US claims to Oregon by ratifying the Russo-American Treaty of 1824, which established Russian Alaska's southern border at 54°40′ north.