The battle of Savannah was fierce, and this was the detonator the Union government in Philadelphia needed to declare war.
The Georgian militia was unable to put a serious resistance to the advance of Spanish regulars from St Augustine and their reinforcements from Cuba, and at the same time control the devastation the invading forces were causing. The defenses of Savannah were attacked from both land and sea. In April 1800 the city surrendered.
This sort of attack was inadmissible for the public opinion in the Union, and while President Jackson, and most politicians in Philadelphia, were convinced that the whole situation was Georgian fault, this was election year.
Britain played the neutrality card, and gave an offer for mediation between the parts. Traditionally Britain would go for anything that would hurt Spain and the USA were an important commercial partner, but the USA were also a rival that should not be allowed to grow to much. Despite things in Europe, mainly in France, were more worrying, and Spain was still an ally in that situation.
The USA had no regular army by this time. After the independence war, states had no supported to much central power, including a Federal Army. There have been some talks about a federal Navy but, at the time of declaration of war, the USA had to rely on privateering. There was few privateers, however, to defend Savannah. So the first line of defense was to send the South Carolina state militias to reinforce the Georgian ones and to organize the defense of Louisville.
The Spanish troops in Georgia decided not to advance further, but rather concentrated in controlling the area near Savannah, and other areas in southern Georgia already occupied. The Spanish tried to break the economy of occupied lands, preventing plantations to operate normally, either by burning them or preventing slaves to work.
The core of the Spanish fleet arrived in June to St Augustine, and soon moved north to Savannah, while the Cuban fleet surrounded the peninsula to reinforce vulnerable spots near the Apalachicola.
In July a fierce counterattack by the Union army caused heavy fatalities in both sides, but the occupation forces kept in control of Savannah, her fortifications and the sea. Plans to march over Louisville were aborted, however.
In Havana, the Spanish strategists were discussing the real aims of the war. While some believed that the USA (without Britain) should be easily defeated and that Spain could claim the land or handle it back to Britain, most people realized that: it would be very hard to have effective control on the whole USA, and any move in that direction would break Britain neutrality.
Some proposed claiming Georgia territory, once part of Florida; or at least the parts of Georgia currently occupied by the Spanish. But there were also many discussion on how important Florida really was. The eastern part, mainly, was of limited interest by the Spanish, and capturing Georgia or parts of her, would probably bring more troubles than anything else.
Prewar status, and clarification what US citizens are allowed to do, and not to do, in Florida was the main goals. Limited territorial claims on Georgia would be put in the negotiation table. The problem was now how to get the USA to negotiate.
Spain kept in control of Savannah till September, repealing occasional raids. Then they deoccupied the farmland and the city, kept control of the fortifications, as well a sizeable fleet in the port, and left definitively in early November. They kept, however, occupation troops in southern Georgia.
The main fleet moved North, keeping off shore of Delaware bay, while a negotiation commission was sent to Philadelphia. Hostilities were officially over with the Christmas Treaty of Philadelphia, the 25th December of 1800.