I lived in Florida for 17 years so I say this with some authority.
The true history of Florida is that it was abandoned by everyone from the Spanish to the US military because it is basically uninhabitable without mosquito repellent and air conditioning. Lacking those inventions, there were no investments or population in Florida of any size. It was a useless swamp.
When oil tycoon Henry Flagler was gifted a friend's property on what is now Biscayne Blvd in return for his promise to build a hotel there for the wealthy patron and her friends, Miami was born. It did not develop much further than the railroads, however, until Flagler's railroad was lost at sea during the Galveston Hurricane and never recovered financially. It's now known that if the Florida Overseas Railroad had operated for 100 years, it still wouldn't reach profitability. Transportation to and from Florida (other than by boat) was a fantasy propped up by oil money. There was still no serious business development. Key West was the capital of Florida for 100 years, if that tells you anything, because it's a port city with better access to the rest of the world than anywhere else in Florida.
What changed all of this was the interstate system. For the first time, Americans had both cars and somewhere to take them. Jackie Gleason famously semi-retired to Miami only to wind up ruthlessly promoting it on a weekly TV show where he encouraged Pennsylvanians and New Jerseyites to leave their snow-covered driveways behind and come down to sunny Florida. Even Disney World's location was selected by Walt because of its easy access to the interstate, meaning guests would come from many states to visit.
Without the failure of the railroad (and its subsequent rebuilding as a freeway) and the connecting interstate to bring people to Florida, along with the charm and influence of Jackie Gleason, Miami would not have become The Magic City -- a name it gets from being the only city in the US which went to "City" status in one step, without ever being a town or settlement or any other geographic designation prior to that. There would be no Disney World. And Miami would not have become the Latam capital that it is. It is, after all, part of US 1, the very first (most important?) of the interstates. To this day, all three of the major north-south routes in the Miami area parallel the original US 1, which still exists in many places, places occupied by about 5 million people. All of that happened because of the interstate.