The nation's first constitution was adopted on 18 July 1830. 19th century At the time of independence, Uruguay had an estimated population of just under 75,000. The political scene in Uruguay became split between two parties: the conservative Blancos (Whites) headed by the second President Manuel Oribe, representing the agricultural interests of the countryside; and the liberal Colorados (Reds) led by the first President Fructuoso Rivera, representing the business interests of Montevideo. The Uruguayan parties received support from warring political factions in neighboring Argentina, which became involved in Uruguayan affairs. The Colorados favored the exiled Argentine liberal Unitarios, many of whom had taken refuge in Montevideo while the Blanco president Manuel Oribe was a close friend of the Argentine ruler Manuel de Rosas. On 15 June 1838, an army led by the Colorado leader Rivera overthrew President Oribe, who fled to Argentina. Rivera declared war on Rosas in 1839. The conflict would last 13 years and become known as the Guerra Grande (the Great War). In 1843, an Argentine army overran Uruguay on Oribe's behalf but failed to take the capital. The siege of Montevideo, which began in February 1843, would last nine years. The besieged Uruguayans called on resident foreigners for help, which led to a French and an Italian legion being formed, the latter led by the exiled Giuseppe Garibaldi. In 1845, Britain and France intervened against Rosas to restore commerce to normal levels in the region. Their efforts proved ineffective and, by 1849, tired of the war, both withdrew after signing a treaty favorable to Rosas. It appeared that Montevideo would finally fall when an uprising against Rosas, led by Justo José de Urquiza, governor of Argentina's Entre Ríos Province, began. The Brazilian intervention in May 1851 on behalf of the Colorados, combined with the uprising, changed the situation and Oribe was defeated. The siege of Montevideo was lifted and the Guerra Grande finally came to an end. Montevideo rewarded Brazil's support by signing treaties that confirmed Brazil's right to intervene in Uruguay's internal affairs. In accordance with the 1851 treaties, Brazil intervened militarily in Uruguay as often as it deemed necessary. In 1865, the Triple Alliance was formed by the emperor of Brazil, the president of Argentina, and the Colorado general Venancio Flores, the Uruguayan head of government whom they both had helped to gain power. The Triple Alliance declared war on the Paraguayan leader Francisco