[5] Unable to deploy French troops during the blockade, France promoted civil wars against Rosas to support the naval actions.

As there was a strong British religious tradition, Rosas was accused of replacing the crosses of churches with his portrait, persecuting religion, and killing priests; and that he may have murdered his wife Encarnación Ezcurra and had incestuous relations with his daughter.

He considered that Rosas would be in contravention of the 4th article of the Mackau-Arana treaty (in which the Confederation recognized the independence of Uruguay) by attempting to impose an Argentine president on it.

[11] Brazilian viscount Miguel Calmon du Pin e Almeida met the British Lord Aberdeen, to request that Brazil join Britain and France in the action against Rosas.

Arana, Deffaudis and Ouseley rejected Brent's mediation, and gave an ultimatum: if the army of Oribe and the Argentine navy of William Brown did not leave Uruguay in ten days, they would proceed to block Buenos Aires.

William Brown requested permission to return to Buenos Aires, which was allowed but with the condition of delivering the British and French sailors.

However, to prevent foreign claims of sovereignty, he left a force of twelve aged crippled soldiers, who would keep the flag of Argentina raised until the end.

They said that Rosas did not stop the war despite their good intentions, or that the capture of the Argentine navy, invasion of Martín García and reinforcement of Montevideo were described in violent language at Buenos Aires newspapers, which was also found at the meeting of the Junta or in the messages that called the Unitarians savages.

Rosas was confident in that this formal declaration, signed by foreign diplomats, would counter the Montevidean propaganda and turn the international opinion to his side.

Those demands were the inclusion of Oribe in the negotiations, disarm of Montevideo, return of Colonia, Martín García and the captured navy, departure from the internal rivers, acknowledgement of the sovereignty of Argentina and an indemnification.

He would write in his memoirs that "the repression of disorder was difficult, considering that Colonia had plenty of resources, and specially of spirituous [liquor] that increased the desires of the virtuous pillagers".

[23][24] The navy moved then to Martín García, 550 French troops defeating the 125-strong army detachment under Colonel Geronimo Costa stationed there.

The pillage of Gualeguaychú was even worse than in Colonia, to the point that Bustamante wrote to Rivera worried about Garibaldi, fearing that his actions would discredit the whole operation.

Garibaldi described that "The city of Gualeguaychú drove us to conquest by being a real emporium of wealth, capable to dress our ragged soldiers and supply us with harnesses.

We acquired many and very good horses in Gualeguaychú, the clothes needed to dress all the people, the harnesses of cavalry and some money distributed among our poor soldiers and sailors, who suffered so much time of misery and privations".

Brazilian newspapers such as O Brado de Amazonas and O Sentinella da Monarchia referred to Rosas as a great South American hero.

He also wrote a letter to the British Morning Chronicle, explaining that a military occupation of Buenos Aires by Anglo-French forces would be nearly impossible.

[41] The return seemed difficult, as many ships were damaged and Mansilla was rearming the north of San Lorenzo, so they requested Montevideo to send reinforcements.

In 1846 the 73rd (Perthshire) Regiment of Foot sailed from Cork, and after docking at Rio de Janeiro, arrived in Montevideo, which it defended for seven months against besieging Argentine troops.

[44] However, unknown to Ouseley, Thomas Samuel Hood was already navigating to Buenos Aires with the opposite instructions from the allied countries: negotiate an end to the hostilities, at whatever price Rosas demanded.

Britain and France sent two new diplomats, John Hobart Caradoc and Alexandre Florian Joseph Colonna, who would pretend to agree with the Hood bases but surreptitiously change the terms.

Britain would return the captured ships, the Martín García island, remove their troops from Uruguay, accept the Argentine sovereignty over its internal waters, and condition the whole treaty to the approval of Oribe.

The parliament was divided in two proposals: to send Lepredour with a very powerful navy, to make a treaty favourable to the French terms by intimidating Rosas, or to openly declare war.

Rosas finally agreed on 31 August 1850, to a pair of small concessions that did not actually modify the important points of the treaty: Rosas would remove the Argentine troops from outside Montevideo at the same time that the foreign legion evacuated Montevideo,[53] but keeping a portion of them during the first months of Oribe's rule to prevent anarchy; and Argentina would refer to Oribe in the document as "President of the Republic" while France would do so as "Brigadier General".

Revisionist authors consider it a key event in the history of Argentina, next to the Argentine War of Independence, while traditional historians disagree.

Luis Alberto Romero considers that the importance of the battle is overrated because it was a defeat: the Anglo-French navy destroyed the artilleries and proceed to the north, as they wanted to do.

The end of the blockade in favourable terms to the Confederation was more the result of a change of policy by the Foreign Office after the appointment of Lord Palmerston than a success of Rosas' diplomacy.

[56] Pacho O'Donnell considers that, even though the combined fleet could force its way, it ultimately failed in its main purposes: they could not turn the Argentine Mesopotamia into a new country, nor gain total control of the Parana River, nor establish their presence in the zone.

He points that the number of casualties in it may be high in the context of the military history of Argentina, but not on a global scale, as it was nowhere near the 1916 Battle of the Somme, with more than 20,000 deaths in just half an hour.

The British expedition, commissioned without parliament authorisation and inconsistent with the non-intervention policy previously declared by the foreign office, then held by Lord Aberdeen, eventually withdrew, largerly under Rosas' terms.