The treaty that resulted in the U.S. acquiring Florida was the Adams-Onís Treaty, signed in 1819 between the United States and Spain. The treaty resolved territorial disputes following the Louisiana Purchase and allowed the U.S. to acquire Florida while also addressing boundary issues in the western territories. In exchange, the U.S. assumed $5 million in claims that American citizens had against Spain. This agreement not only expanded U.S. territory but also marked a significant step in the nation's westward expansion, shaping the future borders and policies of the United States.