The cession of Florida from the Kingdom of Spain to the United States was formalized through the Adams-Onís Treaty, which was signed in 1819 and ratified in subsequent years. The treaty was primarily negotiated between U.S. Secretary of State John Quincy Adams and Spanish Minister Luis de Onís. The background of this transfer involved ongoing tensions and disputes over boundaries and territorial claims in North America following the War of 1812. The U.S. had been expanding its territory and influence, leading to increasing disputes with Spain, particularly concerning the border between the U.S. and Spanish-held territories.

As part of the agreement, Spain relinquished all claims to Florida and agreed on a boundary that defined the borders of Spanish territories in North America. In exchange, the United States agreed to assume $5 million in claims by American citizens against Spain and to renounce any claims on Texas. The cession was driven largely by the realization on Spain's part that it could not effectively manage its North American territories against the pressure exerted by American expansionism. The transfer was completed through a formal ceremony marking the occasion, symbolically representing a new approach to territorial relations in North America.

This territorial transfer had profound implications for both countries. For the United States, it marked the fulfillment of its desire for territorial expansion, providing a strategic advantage in the southeastern regions. Florida would later become a crucial state in the U.S. as new settlers and industries moved in. For Spain, the loss of Florida signaled a continued decline in its influence in the Americas, laying the groundwork for the eventual loss of its remaining territories in the region.