From top left: Battle of Juncal, Battle of Sarandí, Oath of the Thirty-Three Orientals, Battle of Ituzaingó
|Empire of Brazil||
United Provinces of the Río de la Plata|
|Commanders and leaders|
1st Baron of Rio da Prata
Marquis of Barbacena
Viscount of Laguna
Carlos M. de Alvear
Juan Antonio Lavalleja
|27,242 regulars (Brazilian Imperial Army, National Guard, & Imperial Navy troops)||10,500 regulars & militia (Argentine regular military forces and Uruguayan militias)|
|Casualties and losses|
|8,000+ estimated deaths ||About 2,200 estimated deaths |
The Cisplatine War ( Portuguese: Guerra da Cisplatina), also known as the Argentine-Brazilian War ( Spanish: Guerra argentino-brasileña) or in the Argentine and Uruguayan historiography as the Brazil War,  was an armed conflict over an area known as Banda Oriental or the "Eastern Bank" (roughly present-day Uruguay) in the 1820s between the United Provinces of the Río de la Plata and the Empire of Brazil in the aftermath of the United Provinces' independence from Spain.
Led by José Gervasio Artigas, the region known as the Eastern Bank, in the Río de la Plata Basin, revolted against Spanish rule in 1811, against the backdrop of the 1810 May Revolution in Buenos Aires as well as the regional rebellions that followed in response to Buenos Aires' pretense of primacy over other regions of the viceroyalty. In the same context, the Portuguese Empire, then headquartered in Rio de Janeiro, took measures to solidify its hold on Rio Grande do Sul and to annex the region of the former Eastern Jesuit Missions.
From 1814 on, the Eastern Province joined forces with the provinces of Santa Fe and Entre Rios in a loose confederation called the Federal League, which resisted Buenos Aires' authority. After a series of banditry incidents in territory claimed by the Portuguese Empire, the Rio Grande do Sul, Portugal invaded the Eastern Bank in 1816.
Artigas was finally defeated by the Luso-Brazilian troops in 1820 at the Battle of Tacuarembó.  The Portuguese Empire (formally the United Kingdom of Portugal, Brazil and the Algarves since 1815) then formally annexed the Eastern Bank, under the name Cisplatina, with support from local elites. With the annexation, the Portuguese Empire now enjoyed strategic access to Río de la Plata and control of the estuary's main port, Montevideo.
After Brazilian independence, in 1822, the Cisplatina became part of Brazil. It sent delegates to the 1823 Constitutional Convention and, under the 1824 Constitution, enjoyed a considerable degree of autonomy, more so than other provinces of the Empire.
While initially welcoming Portuguese intervention in the rogue Eastern province, the United Provinces of the Río de la Plata eventually urged the local populace to rise up against Brazilian authority, giving them political and material support with a view to reestablishing sovereignty over the region.
Rebels led by Fructuoso Rivera and Juan Antonio Lavalleja carried on resistance against Brazilian rule. In 1825, a Congress of delegates from all over the Eastern Bank met in La Florida and declared independence from Brazil, while reaffirming its allegiance to the United Provinces of the Río de la Plata. In response, Brazil declared war on the United Provinces.
The two navies which confronted each other in the River Plate and the South Atlantic were in many ways opposites. Brazil was a major naval power with 96 warships, large and small, an extensive coastal trade and a large international trade carried on mostly in British, French and American ships. The United Provinces of the Río de la Plata had similar international trading links but had few naval pretensions. Its navy consisted of only half a dozen warships and a few gunboats for port defence. Both navies were short of indigenous sailors and relied heavily on British - and, to a lesser extent - American and French officers and men, the most notable of which were the Argentine commander, the Irish born Admiral William Brown, and the commander of the Brazilian inshore squadron, the English Commodore James Norton. 
The strategy of the two nations reflected their respective positions. The Brazilians immediately imposed a blockade on the River Plate and the trade of Buenos Aires, while the Argentines attempted to defy the blockade using Brown's squadron while unleashing a swarm of privateers to attack Brazilian seaborne commerce in the South Atlantic from their bases at Ensenada and more distant Carmen de Patagones.  The Argentines gained some notable successes - most notably by defeating the Brazilian flotilla on the Uruguay River at the Battle of Juncal and by beating off a Brazilian attack on Carmen de Patagones. But by 1828, the superior numbers of Brazil's blockading squadrons had effectively destroyed Brown's naval force at the Monte Santiago and was successfully strangling the trade of Buenos Aires and the government revenue it generated. 
On land, the Argentine army initially crossed the River Plate and established its headquarters near the Uruguayan town of Durazno. General Carlos María de Alvear invaded Brazilian territory and a series of skirmishes followed. Pedro I of Brazil planned a counteroffensive by late 1826, and managed to gather a small army mainly composed of Southern Brazil volunteers and European mercenaries. The recruiting effort was hampered by local rebellions throughout Brazil, which forced the Emperor to relinquish direct command of his Army, return to Rio de Janeiro and bestow command of the troops on Felisberto Caldeira Brant, Marquis of Barbacena. The Brazilian counteroffensive was eventually stopped at the Battle of Ituzaingó.
Ituzaingó was the only battle of some magnitude in the whole war. A series of smaller clashes ensued, including the Battle of Sarandí, and the naval Battles of Juncal and Monte Santiago. Scarcity of volunteers severely hampered the Brazilian response, and by 1828 the war effort had become extremely burdensome and increasingly unpopular in Brazil. That year, Rivera reconquered the territory of the former Eastern Jesuit Missions.
The stalemate in the Cisplatine War was caused by the inability of the Argentine and Uruguayan land forces to capture major cities in Uruguay and Brazil,  the severe economic consequences imposed by the Brazilian blockade of Buenos Aires,  and the lack of manpower for a full-scale Brazilian land offensive against Argentine forces. There was also increasing public pressure in Brazil to end the war. All of this motivated the interest on both sides for a peaceful solution.
Given the high cost of the war for both sides and the threat it posed to trade between the United Provinces and the United Kingdom, the latter pressed the two belligerent parties to engage in peace negotiations in Rio de Janeiro. Under British and French mediation, the United Provinces of the Río de la Plata and the Empire of Brazil signed the 1828 Treaty of Montevideo, which acknowledged the independence of the Cisplatina under the name Eastern Republic of Uruguay.
The treaty also granted Brazil sovereignty over the eastern section of the former Eastern Jesuit Missions and, most importantly, guaranteed free navigation of the Río de la Plata, a central national security issue for the Brazilians.
In Brazil, the loss of Cisplatina added to growing discontent with Emperor Pedro I. Although it was far from the main reason, it was a factor that led to his abdication in 1831.
Although the war was not a war of independence, as none of the belligerents fought to establish an independent nation, it has a similar recognition within Uruguay. The Thirty-Three Orientals are acknowledged as national heroes, who freed Uruguay from Brazilian presence. The landing of the Thirty-Three Orientals is also known as the "Liberation crusade". 
The war has a similar reception within Argentina, considered as a brave fight against an enemy of superior forces. The Argentine Navy has named many ships after people, events and ships involved in the war. William Brown (known as "Guillermo Brown" in Argentina) is considered the father of the Argentine navy,     and is treated akin to an epic hero for his actions in the war. He is also known as the " Nelson of the Río de la Plata". 
Brazil has had little interest in the war beyond naval warfare buffs. Few Brazilian historians have examined it in detail. The national heroes of Brazil are instead from Brazilian independence, the conflicts with Rosas or the War of the Triple Alliance. 
Despite the role of Britain in the war, and the presence of British naval officials on both sides of the conflict, the war is largely unknown in the English-speaking world. 
- Vale, Brian. "A War Betwixt Englishmen Brazil Against Argentina on the River Plate 1825–1830", I. B. Tauris
- McBeth, Michael Charles. The Politicians Vs. the Generals: The Decline of the Brazilian Army During the First Empire, 1822-1831 (University of Washington Press, 1972) 582pp
- Scheina,Robert L. Latin America's Wars, Volume I: The Age of the Caudillo, 1791–1899, Potomac Books Inc., 2003, ISBN 1574884492
- Donato, Hernâni. Dicionário das Batalhas Brasileiras, Instituicao Brasileira de Difusao Cultural, 1996. ISBN 8534800340 (2nd edition)
- Theotonio Meirelles Da Silva. Historia Naval Brazileira, BiblioBazaar, LLC, 2008
- Brazilian ephemerides, in Portuguese, by the Baron of Rio Branco
- Baldrich, Juan Amadeo. Historia de la Guerra del Brasil, EUDEBA, Buenos Aires, 1974
- Vale, Brian. Una guerra entre ingleses, Instituto de Publicaciones Navales, Buenos Aires, 2005
- Lalonde, Suzanne. Determining boundaries in a conflicted world: the role of UTI possidetis. McGill-Queen's University Press, 2002. Pg 38 – Google Books
- Nahum, Benjamín (1994). Manual de Historia del Uruguay 1830–1903. Montevideo. Editorial De la Banda Oriental.
- Méndez Vives, Enrique (1990). Historia Uruguaya. Montevideo. Editorial De la Banda Oriental.
- Castellanos, La Cisplatina, la Independencia y la república caudillesca, pág. 73–77.
- CARNEIRO, David. História da Guerra Cisplatina. São Paulo: Companhia Editora Nacional, 1946. Pg 38, 59, 70, 112 and 114.
- Doratioto (2002)
- LUSTOSA, Isabel. D. Pedro I. São Paulo: Companhia das Letras, 2007, p.277
- MAGNOLI, Demétrio. O corpo da pátria: imaginação geográfica e política externa no Brasil (1808-1912). São Paulo: EDUNESP, 1997.
- Juan Beverina (1927). La guerra contra el Imperio del Brasil (in Spanish). Biblioteca del Oficial, Bs. As.
- Brian Vale, "A War Betwixt Englishmen Brazil Against Argentina on the River Plate 1825–1830", I. B. Tauris, 2000, pp 13-28
- Brian Vale, "A War Betwixt Englishmen Brazil Against Argentina on the River Plate 1825–1830", I. B. Tauris, 2000, pp 69-116
- Brian Vale, "A War Betwixt Englishmen Brazil Against Argentina on the River Plate 1825–1830", I. B. Tauris, 2000, pp 135-206
- SCHEINA, Robert L. Latin America's Wars: the age of the caudillo, 1791–1899, Brassey's, 2003.
- The economic effects of the blockade
- Uruguay educa Archived 2011-12-03 at the Wayback Machine (in Spanish)
- Spanish: El padre de la Armada Argentina. Used mainly in Argentina but also in other countries like the United Kingdom, see e.g. this BBC report. URL accessed on October 15, 2006.
- Spanish: Guillermo Brown or Almirante Brown, see e.g. his biography at Planeta Sedna. URL accessed on October 15, 2006.
- Irish: Béal Easa, see report at County Mayo's official website. URL accessed on October 15, 2006.
- Irish: Contae Mhaigh Eo, according to its official website. Archived 2011-08-13 at the Wayback Machine URL accessed on October 15, 2006.
- Brian Vale, Una guerra entre ingleses, page 297
- Brian Vale, Una guerra entre ingleses, page 298
- Media related to Cisplatine War at Wikimedia Commons