Before the Europeans arrived, many Atlantean tribes lived in Florida; the largest among them were the Ais, the Apalachee, the Calusa, the Timucua and the Tocobago. 1492 (SCNR), a Castillian expedition (well, it was funded by the king, and some of his people were on the ship, but since the Portuguese had insisted, the captain and all the sailors were Portuguese - Castillians weren't allowed to build caravels) crossed the Atlantic, made landfall in Florida (which was named the same way ITTL), claimed it for Castille-Portugal. Soon, the colony was expanded, and north of it, Virginia (named after the Virgin Mary; OTL Georgia) was founded.
1562, King Henry IV of the Triple Monarchy of England-Castille-Portugal appointed a viceroy residing at Santiago (at OTL Havana's site) who coordinated governmental activities in the five capitanates / captainships (these being Caribbea, Texas, Mayaland, Florida and South Atlantis).
After the split of the Triple Monarchy, Florida stayed in the hands of Spain; but since 1629, the Spanish were thrown out of Virginia by the French.
In the anti-French War, several smaller fights were fought in north Florida; and in 1692, Friedrich von Hohenzollern, a German in the service of the governor of Italia Nuova, made "the Wild Ride", fought his way through the French colony of Caroline with his cavalry troops, finally linking up with the Spaniards in Florida. In the peace of Amsterdam, Virginia was returned to Florida.
In 1794, after Spain had been conquered by republican France, Florida declared independence, as did the other Spanish colonies. But as soon as 1812, king Gioacchino of Italy had conquered Florida by his general and later successor Alessandro Napoleoni, now uniting all of OTL Old South.