The Georgian militia was unable to put up serious resistance to the advance of the Spanish regulars from Saint Augustine and a second force from Cuba. The defenses of Savannah were therefore attacked from both land and sea and in April 1800 the city surrendered.
The strength of the assault on fellow Americans in Georgia inflamed public opinion in the Union, and while President Jefferson and most politicians in Philadelphia were convinced that the whole situation was Georgian fault, it was an election year and they had to take their electors views into account in their decisions and declared war on Spain.
Britain played the neutrality card and offered to mediation between the parties. Traditionally Britain had been ready to attack Spain and they had found themselves on opposing sides in many wars, while the U. S. of A. was an important commercial partner, although there was also the a consideration that the U. S. of A. was a potential rival whose growth should be constrained. In addition, there were difficulties in Europe, in particular with France, causing concerns, and in this case Spain was an ally seeking to restrain a bellicose France.
The U. S. of A. had no regular federal army at this time because when independence had been achieved, the states wanted to minimise the centralisation of power in the Federal government, at that included the setting up of a regular Federal Army. There had been some talks about establishing a federal Navy but at the time of declaration of war the U. S. of A. had to rely on privateers. There was however to few privateers to attempt to defend Savannah. So the first line of defense was to send the South Carolina state militias to reinforce the Georgian ones and organize the defense of Louisville.
The Spanish troops in Georgia decided not to advance further, but concentrated their efforts in controlling the area near Savannah and the other occupied areas of southern Georgia. Aware that they might be forced back when other US forces arrived, the Spanish tried to break the economy of occupied lands by destroying the plantations.
The core of the Spanish fleet arrived at St Augustine in June and promptly 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 hastily raised Union army caused heavy fatalities on both sides, but the Spanish occupation forces kept control of Savannah, her fortifications and the sea, although plans to march to Louisville were however abandoned.
In addition to their immediate actions, the Spanish strategists Havana, discussed were discussing longer term aims for the war. While some believed that the U. S. of A. (without British support) could be easily defeated and that Spain would be able to control the land, or use the conquered land in their negotiations with the British, most people realized that it would be very hard to gain effective control on the whole USA, and that if they did Britain main become concerned and revoke its position of neutrality and intervene on the side of the US.
Some proposed claiming Georgia territory as it had once part of Florida; or at least the parts of Georgia currently occupied by Spanish speakers, there were also many discussion about the real importance of Florida. The eastern area in particular of limited interest to the Spanish and capturing parts of Georgia would probably bring more troubles than benefits.
Reinforcement of the Prewar status of the Georgia and Florida and clarification of the rights and responsibilities of US citizens involved with Florida became the main goals for the negotiation table together with limited territorial claims on Georgia. The problem became how could the USA be enticed, or forced, to negotiate.
Spain kept in control of Savannah until September, repelling occasional raids. Then they evacuated the farmland and the city although control of its fortifications was kept until early November when together with a sizable fleet that had remained in the port the remaining troops departed the area. Occupation troops were however to remain in southern Georgia.
The main fleet moved North until it reached Delaware Bay where it remained a position of threat while a negotiation commission was sent to Philadelphia resulting in the Christmas Treaty of Philadelphia, the 25th December of 1800. when hostilities were declared over.