In 1851 the Argentine provinces of Corrientes and Entre Rios raised an army to overthrow the Argentine dictator Juan Manuel de Rosas. The Liberation Army was led by Justo Jose Urquiza; Brazil and the Colorados (Liberals) of Uruguay formed an alliance with them. Their first aim was overthrow the Blancos (Conservatives) in Uruguay and thus eliminate Rosas' ally. In July 1851, while the Imperial Fleet cut the communications between Rosas and his ally by taking control of La Plata river, Urquiza's troops entered Uruguay. On September 6, 1851, the Brazilian Imperial Army entered Uruguay in support. Surrounded by overwhelming enemy forces, Oribe, leader of the Blanco Party, surrendered without much fighting on October 8, 1851. Uruguay now fell under the control of the Colorados, led by Joaquin Suarez. From October until December, 1851 the Allies strengthened their position by making contact with other Argentines discontent with Rosas. New volunteers joined the Liberation Army.
Meanwhile, the Brazilian Imperial Navy blockaded Buenos Aires. Rosas had no hope of receiving supplies and ammunition from abroad. Nevertheless, the Allies expected a long campaign on land. Furthermore, the possibility of the presence of the Imperial Army of Brazil on Argentine soil threatened to undo the provincial alliance against Rosas. An resolution was achieved when the Allied command established that Urquiza would be the commander-in-chief of the Liberation Army. He would lead the army into Argentina. The bulk of the Imperial Army (some 10,000 men) would be placed in Uruguay as reserve. For political reasons Urquiza expected not to be forced to make use of them for fear of the anti-Brazilian feeling in some of Argentinean provinces. Urquiza himself would lead some 27,000 troops ( 2,000 Uruguayans; 4,000 Brazilians; and 21,000 Argentineans). The Imperial Navy would be kept in the nearby in order to land the reserves, if necessary, and give support when possible.
On December 23, 1851 the Allies began to march into Argentina. Contrary of expectations, no serious opposition was made by Rosas forces. By February 1, 1852 the Liberation Army camped in the vicinity of Buenos Aires. Urquiza had an army of 25,000 men available (1000 artillery, 16,000 cavalry and 8000 infantry) and 45 cannons. The following day Rosas army marched towards the enemy, deploying his troops on the Caseros hills. Rosas was at the head of his army with 22,000 men (1000 artillery, 13,000 cavalry and 8000 infantry) and 56 guns. Almost immediately the vanguard of the two armies started firing at each other.
The Battle of Caseros began on February 3, 1852. Fighting began at some time between 0800 and 1000. By 1300 in the afternoon the last shots were heard. The battle was over. The Liberation Army had conquered the enemy position. The Liberation Army captured about seven thousand prisoners. Rosas was not among them. He had escaped with some of his officers just some minutes before his army gave way, getting aboard a British ship on that same night. He would never return to Argentina again.
On the February 18, 1852, Urquiza entered Buenos Aires, taking control of the national government.
According to Brazilian sources, the Allied army's casualties amount to some 400 killed, and an un specified number of wounded. The Uruguayan Division had one officer and three soldiers killed. One officer and 14 soldiers were wounded. The Imperial Army losses on the battlefield were as follows: 14 dead (including one officer), 55 wounded and five missing. Later one officer and some soldiers died from the receiving wounds. The information is not exact and these numbers maybe underestimates. The Argentinean casualties are not given neither among Rosas forces nor among the Liberation Army. But according to one, Rosas army may have suffered some 1,200 dead while the number of captured officers and soldiers was considerably higher.