French blockade of the Río de la Plata

1841 portrait by Cayetano Descalzi of the Argentine Juan Manuel de Rosas, who emerged victorious in the conflict against France

Date	1838-1840
Location	Río de la Plata
Result	Argentine victory

Belligerents

Argentine Confederation
Supported by:

Blancos

France
Supported by:

Unitarians

Colorados

The French blockade of the Río de la Plata was a two-year-long naval blockade imposed by France on the Argentine Confederation ruled by Juan Manuel de Rosas. It closed Buenos Aires to naval commerce. It was imposed in 1838 to support the Peru–Bolivian Confederation in the War of the Confederation, but continued after the end of the war. France didn't land ground forces, but instead took advantage of the Uruguayan Civil War and the Argentine Civil Wars, supporting Fructuoso Rivera and Juan Lavalle against Manuel Oribe and Rosas.

After two years without the expected results, France signed the Mackau-Arana treaty with the Argentine Confederation, ending the hostilities.

The Peru–Bolivian Confederation declared the War of the Confederation over Argentina and Chile. His Supreme Protector Andrés de Santa Cruz supported the European interests in South America, as well as the Unitarians, whereas Rosas and the Chilean Diego Portales did not. As a result, France gave full support to Santa Cruz in this war. Britain also supported Santa Cruz, but only by diplomatic meanings. Trusting in the military power at his disposal, Santa Cruz declared war to both countries at the same time. Initially, the Peru-Bolivian forces had the advantage, and captured and executed Portales. The war did not develop favourably for Argentina in the north, and the French consul Aimé Roger moved to Buenos Aires to request the capitulation of Argentina. He demanded that a pair of French citizens were released from prison. Those were César Hipólito Bacle, who had sold Argentine cartography to Bolivia, and Pedro Lavié, who had stolen from a regiment in Dolores. It was also demanded that another pair were exempted from military service, and that France received the condition of "most favoured nation". This designation would provide commercial privileges, similar to those granted by Bernardino Rivadavia to Britain. Although the requests were light, Rosas considered that they would only provide precedent for further French interference in the internal affairs of Argentina, and refused to comply. As a result, France started a naval blockade over Buenos Aires. The French admiral Louis François Jean Leblanc started it on March 28, 1838.

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