036–States and Territories of the United States of America (July 10, 1821 to August 10, 1821)

July 10, 1821: The Adams-Onís Treaty or Transcontinental Treaty came into effect, establishing a defined border between the United States and New Spain. The treaty ceded Spain’s claims to Oregon Country to the United States and American claims to Texas to Spain; moved portions of present-day Colorado, Oklahoma, and Wyoming, and all of New Mexico and Texas, to New Spain; and all of Spanish Florida to the United States. The new borders intruded on Arkansaw Territory’s Miller County, created on April 1, 1820, which dipped below the Red River and into land now ceded to Spain. However, the remoteness of the region caused no serious conflict with Spain.