The Argentinian blockade of Montevideo was ineffective as Rosas generally tried not to interfere with international shipping on the River Plate but, in 1845, when access to Paraguay was blocked, Great Britain and France allied against Rosas, seized his fleet and began a blockade of Buenos Aires, while Brazil joined in the war against Argentina. Rosas reached peace deals with Great Britain and France in 1849 and 1850 respectively. The French agreed to withdraw their legion if Rosas evacuated Argentinian troops from Uruguay. Oribe still maintained a loose siege of the capital. In 1851, the Argentinian provincial strongman Justo José de Urquiza turned against Rosas and signed a pact with the exiled Unitarios, the Uruguayan Colorados and Brazil against him. Urquiza crossed into Uruguay, defeated Oribe and lifted the siege of Montevideo. He then overthrew Rosas at the Battle of Caseros on 3 February 1852. With Rosas's defeat and exile, the "Guerra Grande" finally came to an end. Slavery was officially abolished in 1852. A ruling triumvirate consisting of Rivera, Lavalleja and Venancio Flores was established, but Lavalleja died in 1853, Rivera in 1854 and Flores was overthrown in 1855.