Question: What was the capital of the union of provinces in the Río de la Plata comprised by most of the former dependencies from the last to be organized and also the shortest-lived of the Viceroyalties of the Spanish Empire in the Americas?

full_context: Document 1: Puerto Madero: Puerto Madero, also known within the urban planning community as the Puerto Madero Waterfront, is a barrio (district) of the Argentine capital at Buenos Aires CBD, occupying a significant portion of the Río de la Plata riverbank and representing the latest architectural trends in the city of Buenos Aires.
Document 2: Club Atlético River Plate: Club Atlético River Plate is an Argentine sports club based in the Belgrano neighborhood of Buenos Aires, and named after the city's estuary, Río de la Plata. Although many sports are practiced at the club, River is best known for its professional football team, which has won the most domestic competitions in Argentina with 36 league titles in the top division, 2 second division championships and 9 national cups. At international level, River Plate has won a total of 16 official titles.
Document 3: Governorate of the Río de la Plata: The Governorate of the Río de la Plata (1549−1776) (Spanish: "Gobernación del Río de la Plata" ) was one of the governorates of the Spanish Empire. It was created in 1549 by Spain in the area around the Río de la Plata.
Document 4: List of heads of state of Argentina: Argentina has had many different types of heads of state, as well as many different types of government. During Pre-Columbian times the territories that today form Argentina were inhabited by nomadic tribes, without any defined government. During the Spanish colonization of the Americas, the King of Spain retained the ultimate authority over the territories conquered in the New World, appointing viceroys for local government. The territories that would later become Argentina were first part of the Viceroyalty of Peru, and then the Viceroyalty of the Río de la Plata. The May Revolution started the Argentine War of Independence by replacing the viceroy Baltasar Hidalgo de Cisneros with the first national government. It was the Primera Junta, a junta of several members, which would grow into the Junta Grande with the incorporation of provincial deputies. The size of the Juntas gave room to internal political disputes among their members, so they were replaced by the First and Second Triumvirate, of three members. The Assembly of the Year XIII created a new executive authority, with attributions similar to that of a head of state, called the Supreme Director of the United Provinces of the Río de la Plata. A second Assembly, the Congress of Tucumán, declared independence in 1816 and promulgated the Argentine Constitution of 1819. However, this constitution was repealed during armed conflicts between the central government and the "Federal League" Provinces. This started a period known as the "Anarchy of the Year XX", when Argentina lacked any type of head of state.
Document 5: Historiography of the May Revolution: Historiographical studies of the May Revolution started in the second half of the 19th century in Argentina and have extended to modern day. All historiographical perspectives agree in considering the May Revolution as the turning point that gave birth to the modern nation of Argentina, and that the Revolution was unavoidable in 1810. The main topics of disagreement between Argentine historians are the specific weight of the diverse causes of the May Revolution, who were the leaders of it among the different involved parties, whenever there was popular support for it or not, and whenever the loyalty to the captive Spanish king Ferdinand VII was real or an elaborate masquerade to conceal pro-independence purposes.
Document 6: Argentine Confederation: The Argentine Confederation (Spanish: "Confederación Argentina") is one of the official names of Argentina according to the Argentine Constitution, Article 35. It was the name of the country from 1831 to 1852, when the provinces were organized as a confederation without a head of state. The governor of Buenos Aires Province (Juan Manuel de Rosas during most of the period) managed foreign relations during this time. Under his rule, the Argentine Confederation resisted attacks by Brazil, Bolivia, Uruguay, France and the UK, as well other Argentine factions during the Argentine Civil Wars.
Document 7: History of the regional distinctions of Spain: For many years the Spanish monarchy and the dictatorships which followed—Primo de Rivera and Franco—maintained the position that Spain was a unified nation, the legacy of the Roman province, Hispania. In reality, Spain (formerly known as the Spains) is and has long been a cluster of different territories with their own systems. Currently, Spain is divided into eighteen autonomous entities, which are themselves composed of fifty provinces. Seven of those eighteen autonomous entities are officially designated as "nationalities", while the rest are defined as regions, historical regions, communities and historical communities. There are many proponents of this confederacy, however it does carry certain historical problems. Just as neither modern nor historical Spain were a single unit, the modern divisions also do not really work in the past. Nonetheless, modern Spain is more easily understood when one first understands the differences which underlie its current divisions.
Document 8: United Provinces of the Rio de la Plata: The United Provinces of the Río de la Plata (Spanish: "Provincias Unidas del Río de la Plata" ), earlier known as the United Provinces of South America (Spanish: "Provincias Unidas de Sudamérica" ), a union of provinces in the Río de la Plata region of South America, emerged from the May Revolution in 1810 and the Argentine War of Independence of 1810–1818. It comprised most of the former Viceroyalty of the Río de la Plata dependencies and had Buenos Aires as its capital.
Document 9: State of Buenos Aires: The State of Buenos Aires ("Estado de Buenos Ayres") was a secessionist republic resulting from the overthrow of the Argentine Confederation government in the Province of Buenos Aires on September 11, 1852. The State of Buenos Aires was never recognized by the Confederation or by foreign nations; it remained, however, nominally independent under its own government and constitution. Buenos Aires rejoined the Argentine Confederation after the former's victory at the Battle of Pavón in 1861.
Document 10: Viceroyalty of the Río de la Plata: The Viceroyalty of the Río de la Plata (Spanish: "Virreinato del Río de la Plata" ) was the last to be organized and also the shortest-lived of the Viceroyalties of the Spanish Empire in the Americas.
Document 11: Argentina: Argentina ( ; ] ), officially the Argentine Republic (Spanish: "República Argentina" ), is a federal republic in the southern portion of South America. Sharing the bulk of the Southern Cone with its neighbor Chile to the west, the country is also bordered by Bolivia and Paraguay to the north, Brazil to the northeast, Uruguay and the South Atlantic Ocean to the east, and the Drake Passage to the south. With a mainland area of 2780400 km2 , Argentina is the eighth-largest country in the world, the second largest in Latin America, and the largest Spanish-speaking one. The country is subdivided into twenty-three provinces (Spanish: "provincias" , singular "provincia") and one autonomous city ("ciudad autónoma"), Buenos Aires, which is the federal capital of the nation (Spanish: "Capital Federal" ) as decided by Congress.
Document 12: Governorate of Paraguay: The Governorate of Paraguay (Spanish: "Gobernación del Paraguay" ), originally called the Governorate of Guayrá, was a governorate of the Spanish Empire and part of the Viceroyalty of Peru. Its seat was the city of Asunción; its territory roughly encompassed the modern day country of Paraguay. The Governorate was created in December 16, 1617 by the royal decree of King Philip III as a split of the Governorate of the Río de la Plata and of Paraguay into its respective halves. The Governorate lasted until 1782, after which the massive Viceroyalty of Peru was split, and Paraguay became an intendency ("intendencia") of the new Viceroyalty of the Río de la Plata.
Document 13: Río de la Plata: The Río de la Plata (] , "River of Silver") — rendered River Plate in British English and the Commonwealth and La Plata River (occasionally Plata River) in other English-speaking countries — is the river and estuary formed by the confluence of the Uruguay and the Paraná rivers. It empties into the Atlantic Ocean, forming a funnel-shaped indentation on the southeastern coastline of South America. Depending on the geographer, the "Río de la Plata" may be considered a river, an estuary, a gulf or a marginal sea. For those who consider it a river—as is the case in most of Argentina and Uruguay—it is the widest river in the world, with a maximum width of about 220 km .
Document 14: Buenos Aires: Buenos Aires ( or ; ] ) is the capital and most populous city of Argentina. The city is located on the western shore of the estuary of the Río de la Plata, on the South American continent's southeastern coast. "Buenos aires" can be translated as "fair winds" or "good airs", but the first one was the meaning intended by the founders in the 16th century, by the use of the original name "Real de Nuestra Señora Santa María del Buen Ayre". The Greater Buenos Aires conurbation, which also includes several Buenos Aires Province districts, constitutes the fourth-most populous metropolitan area in the Americas, with a population of around 17 million.
Document 15: Real Audiencia of Charcas: The Real Audiencia of Charcas (Spanish: "Audiencia y Cancillería Real de La Plata de los Charcas" ) was a Spanish "audiencia" with its seat in what is today Bolivia. It was established in 1559 in Ciudad de la Plata de Nuevo Toledo (later Charcas, today Sucre) and had jurisdiction over Charcas, Paraguay and the Governorate of the Río de la Plata, today Uruguay and northern Argentina. This court oversaw the incredible silver output of the mines at Potosí. It was part of the Viceroyalty of Peru until 1776, when it was transferred to the newly created Viceroyalty of the Río de la Plata and began to be referred to as Upper Peru.
ground_truth: Buenos Aires