Present day South America is made up extensively of Spanish speaking countries, a speckle of English, Dutch and French in the north east, and the biggest country of Brazil speaking Portuguese, however the map of South America, circa 1750 looked much different. The whole west coast from what is now Venezuela down to the southern parts of Chile had been explored and settled by the Spanish; where as the east, following the main waterways and rivers, had been almost completely settled by the Portuguese. The central parts of the country having to be explored by foot or horseback, were still up for grabs, but the precious territory was the coast.
As this exploration increased, and countries began to solidify borderies, territories and constitutions, Uruguay, known then as Banda Oriental, acted as a buffer zone between the expanding Portuguese Brazil to the northeast, and the United Provinces of the Rio de La Plata, soon to be Argentina, to the south west. The mother countries of these two infant nations, Spain and Portugal, wanted to cash in their chips, stake a claim to the Banda Oriental, and keep some of their empire in South America.
After the current day capital of Montevideo was changing hands, patrio Jose Gervasio Artigas, a famed figured in the history of Uruguay, had helped form the League of the Free People, he spearheaded a land reform and split up land to farmers. Portugal, not wanting this spreading to the colony of Brazil, ordered an invasion of the territory, known as the Portuguese Conquest of the Banda Oriental. The well trained, and well equipped troops from Brazil took over the territory, and incorporated it as Cisplatina, the southernmost province of Brazil.
At this time, a revolutionary military group, known as the Treinta y Tres Orientales, led by Juan Antonio Lavalleja, who fought alongside Jose Gervasio Artigas, descended upon Cisplatina to organize an alliance with Rio de La Plata, and secede from the Empire of Brazil. The Brazilians responded and sparked the Cisplatine War to defend their newest territory.
The war lasted almost two years and eight months resulting in the Treaty of Montevideo, and although the constitution was not solidified for another year, both countries of Argentina, and Brazil agreed to recognize the territory between them, as the independent country of Uruguay.