The Adams–Onís Treaty, often seen as a pivotal moment in U.S. territorial expansion, was finalized in 1819 as Spain relinquished Florida to the United States for $5 million. This agreement stemmed from a series of conflicts and negotiations concerning border disputes and issues related to Native American lands in the region. As tensions arose due to the Seminole Wars, the United States sought to assert its influence over Florida, which had long been a refuge for fugitive slaves and a home to Native American tribes. The negotiations were led by John Quincy Adams, who had a vision for expanding U.S. territories and strengthening its security. On the other side of the negotiation table was Spanish Minister Luis de Onís, who recognized, after numerous conflicts, that maintaining control over Florida was becoming increasingly untenable for Spain.

The treaty not only facilitated the transfer of Florida but also defined the boundary between Spanish territory and the United States. The agreement also resolved claims both countries had against each other, helping to foster a period of goodwill between the U.S. and Spain. The acquisition of Florida was viewed as part of the United States' manifest destiny, underscoring the belief that it was destined to expand across the continent. Furthermore, the treaty had significant implications for the Native American populations in Florida and the surrounding regions, as U.S. expansion would lead to further displacement and conflict for these groups in the ensuing years.