Oribe, with the support of Buenos Aires strongman Juan Manuel de Rosas, organized a new army and invaded Uruguay, thus starting the Uruguayan Civil War. In December 1842 Oribe defeated Rivera at the Battle of Arroyo Grande and started the Great Siege of Montevideo. Rivera's power was limited to the capital city, while Oribe ruled the rest of the country. In 1847 Rivera was forced to leave for exile in Brazil, where he stayed until 1853.