Question

what was the event leading Florida to becoming part of the U.S.?

Answer 1

The event leading Florida to becoming part of the U.S. was the Adams-Onís Treaty of 1819. The treaty was signed between the United States and Spain, where Spain ceded Florida to the U.S. in exchange for the U.S. dropping its claims on Texas. The treaty was ratified in 1821, officially making Florida a U.S. territory.