The response of the Spanish King Charles III 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, 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 six warships, six frigates, a number of smaller ships and a hundred 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 20 November 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 sent 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 Port Jackson.
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 died and his daughter and successor Maria I dismissed Pombal and concluded on 1 October 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, which the Portuguese had founded in 1680,, with the rest of the Banda Oriental, and also kept the Misiones Orientales. In return, Spain acknowledged that the Portuguese territories in Brazil extended far west of the line that had been set in the Treaty of Tordesillas. In the Treaty of El Pardo, signed on 11 March 1778, Spain won Spanish Guinea, which would be administered from Buenos Aires from 1778 to 1810.
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. Instead Portugal joined the First League of Armed Neutrality in 1781, to resist British seizures of cargo from neutral ships.
