Florida's acquisition by the United States was a complex process involving strategic interests, diplomatic negotiations, and military conflicts. The Adams-Onís Treaty of 1819 secured Florida for the U.S., ending Spanish control and paving the way for American expansion in the Southeast. The territorial period from 1821 to 1845 saw rapid changes in Florida's economy, society, and governance. These changes included population growth, agricultural development, and conflicts with Native Americans, ultimately leading to Florida's statehood in 1845.