A conflict in Look to the West.
The First Platinean War was primarily a Hispano-Portuguese conflict, with Britain supporting Portugal. Spain had hoped for French support, but France was distracted by European affairs at the time.
The war stemmed from tensions over the Treaty of Madrid (1750) which had, ironically, been a project intended to avoid fututre Hispano-Portuguese colonial wars. Having altered the Torsedillas division between Spanish and Portuguese colonies in South America to better reflect the situation on the ground, the final treaty nonetheless required some movement of colonists. This was exacerbated by the Spanish government, under the anti-clericalist policies of the Marquis of Ensenada, ejecting the Jesuits from the Empire and thus abolishing the Seven Jesuit Missions north of the River Plate. Although the Jesuits agreed to go, the Guarani Indians they had been living among were not, and thus Spain and Portugal fought on the same side against the Guarani in the minor Guarani War. The conflict nonetheless soured Hispano-Portuguese relations. Then Joseph I succeeded to the throne of Portugal and appointed Sebastião José de Carvalho e Melo as chief minister. Carvalho proceeded to violate the Treaty and this deteriorated into war not long after the end of the Third War of Supremacy.
The conflict saw the Spanish armies held back in Iberia proper by Anglo-Portuguese forces, this defiance providing a suitable national rallying point for Portugal after the catastrophe of the 1755 Lisbon earthquake. The Spanish were more successful in South America, although their attempt to invade Isla Santa Catarina was defeated by an Anglo-Portuguese force. A British attempt to occupy the mouth of the River Plate failed due to strong resistance on the part of local colonial militiamen - a fiasco which resulted in the controversial execution of Admiral Arbuthnot, and led to the rise of a Platinean national consciousness.
The war ended with status quo ante bellum, except for the fact that Spain gave up Florida to the Empire of North America. In the aftermath of the war, with the death of Joseph I of Portugal and the disappointing performance of Spain, both Iberian chief ministers were exiled to South America and their writings from exile would also influence the Second Platinean War of a generation later.