British expeditionary force invades Buenos Aires on the Río de la Plata

Background. The invasions took place between 1806 and 1807, as part of the Napoleonic Wars and the War of the Third Coalition, at a time when Spain was an ally of Napoleonic France. The United Kingdom judged 1805, after the defeat of the Franco-Spanish fleet at the Battle of Trafalgar, the right moment to act. Proposals for the enterprise had been discussed in 1804 by William Pitt, Lord Henry Melville, Francisco de Miranda and Sir Home Riggs Popham; in 1805 Popham received orders to escort the David Baird-led expedition against the Cape of Good Hope, which was allied with Napoleon.

Occupation and Expulsion. British forces took Quilmes on 25 June 1806 and occupied Buenos Aires on 27 June. The detachment held the city for 46 days before being expelled. The occupation was ended by an army from Montevideo led by Santiago de Liniers, who landed at Las Conchas on 4 August 1806. Liniers advanced with a mixed force of line troops and militia to retake the city.

Historiographical Significance. In Argentine historiography, the two successive defeats of the British expeditionary forces are known collectively as the Reconquista and the Defensa respectively, the Reconquista referring to the first defeat in 1806. In commemoration of the 1806 victory and, by extension, of the campaign as a whole, 12 August is celebrated in Argentina as the day of the "Reconquista de Buenos Aires". Santiago de Liniers was later chosen as new viceroy and prepared the city against a possible new British attack, repelling a second invasion in 1807.