The event that led to the U.S. acquiring Florida from Spain was the Adams-Onís Treaty, negotiated in 1819 and ratified in 1821. Tensions over border disputes and warfare with indigenous peoples created an environment conducive to U.S. interests in Florida. The treaty ceded Florida to the U.S. in exchange for financial compensation to Spain and the U.S. renouncing any claims to Texas. The acquisition not only expanded U.S. territory but also aimed to reduce conflict in the southeastern region and assert American influence in North America, showcasing early expansionist policies.