Spanish–Portuguese War (1776–77)

The Spanish-Portuguese War was fought between 1776-1777 over the border between Spanish and Portuguese South America.

Portuguese attack
In the previous Spanish-Portuguese War, 1761-1763, Spain had conquered the Colonia del Sacramento, Santa Tecla, San Miguel, Santa Teresa and Rio Grande de São Pedro in the First Cevallos expedition.

Colonia del Sacramento was returned to Portugal in the Treaty of Paris, but Santa Tecla, San Miguel, Santa Teresa and Rio Grande de São Pedro remained in Spanish hands, much to the frustration of the Portuguese.

They started assembling troops and harassing the Spanish as early as 1767. Over the years the Portuguese built up an army of 6,000 men, considerably more than the 1,450 Spanish troops in the area. The matter escalated in February 1776 when two Portuguese fleets under Robert MacDouall and Jorge Hardcastle landed troops near the fortress of Rio Grande de São Pedro, and started shelling the place. A Spanish fleet under Francisco Javier Morales came to their help with a naval battle as result. After 3 hours of battle the Spanish had 16 killed and 24 wounded, while the Portuguese lost two vessels.

After this sea-battle, Portuguese land forces pushed forward and the Spanish commander Juan José de Vértiz y Salcedo was forced to withdraw and give up the entire Rio Grande area.

Spanish response
The response of the Spanish King Charles III of Spain was swift. There was little fear that Portugal's old ally Great Britain would come to their aid, as it was fully occupied by the American Revolutionary War.

King Charles III promoted Governor Pedro Antonio de Cevallos to Viceroy of the Río de la Plata and gave him the leadership of the expedition. Cevallos had already proven his ability in the First Cevallos expedition (1762–1763), when he had conquered Colonia del Sacramento and had marched deep into Portuguese territory.

Cevallos was in Spain and organized personally the expedition from Cadiz. He had 9,000 men, and a fleet of 6 warships (Poderoso, 70 guns, Santiago la América, 64, San Dámaso, 70, Septentrión, 70, Monarca, 70,  and San José, 70), 6 frigates, a number of smaller ships and 100 transport ships at his disposal. The commander of the fleet was Francisco Javier Everardo Tilly y García de Paredes, marqués de Casa Tilly. The fleet left Cadiz on November 20 and arrived in South America on 18 February 1777, capturing several Portuguese ships on the way.

There they encountered the Portuguese fleet of Robert MacDouall, which was much smaller and managed to escape.

Cevallos decided to attack the island of Santa Catarina on 23 February. When the Portuguese saw the formidable Spanish fleet disembark their troops, the garrison fled to the mainland without firing a shot. On 20 March, Cevallos sailed towards his second target, Rio Grande de São Pedro, but the fleet was dispersed by a storm and had to return to Montevideo.

There he split up his forces. He sailed himself with all the artillery to Colonia de Sacramento, where he started the siege on 23 May. The city capitulated on 3 June.

The rest of the fleet was send to check the fleet of MacDouall, which was still a menace to be counted with. In fact this fleet surprised and captured the lone San Agustín, and renamed the ship Santo Agostinho. The new captain, who also played an important role in capturing the ship was an Englishman in Portuguese service, Arthur Phillip who later founded the city of Sydney. After the capture of Sacramento, Cevallos marched his troops towards Rio Grande de São Pedro, joined forces with the troops of Juan José Vertiz which were concentrated in Santa Teresa. Then he was ordered to stop his advance, as peace negotiations were started.

Peace
On 24 February 1777 King Joseph I of Portugal died and his daughter and successor Maria I of Portugal concluded on October 1 the First Treaty of San Ildefonso with Spain.

Spain returned the island of Santa Catarina to Portugal and recognized Rio Grande de São Pedro as Portuguese territory, but kept Colonia del Sacramento, Banda Oriental, and Misiones Orientales.

Aftermath
One of the results of the war was that the Portuguese remained neutral when the American War of Independence became a global war in 1778 with the entry of the French. The Portuguese were bound to the British by treaty but disappointed by the lack of British support against Spain, Portugal did not itself enter the war.