Spaniards on 18 May 1811 at the Battle of Las Piedras and began Siege of Montevideo. At this point, Spanish viceroy invited Portuguese from Brazil to launch a military invasion of Banda Oriental. Afraid to lose this province to the Portuguese, Buenos Aires made peace with the Spanish viceroy. British pressure persuaded the Portuguese to withdraw in late 1811, leaving the royalists in control of Montevideo. Angered by this betrayal by Buenos Aires, Artigas, with some 4,000 supporters, retreated to Entre Ríos Province. During the Second Banda Oriental campaign in 1813, Artigas joined José Rondeau's army from Buenos Aires and started the second siege of Montevideo, resulting in its surrender to Río de la Plata. Artigas participated in the formation of the League of the Free People, which united several provinces that wanted to be free from the dominance of Buenos Aires and create a centralized state as envisaged by the Congress of Tucumán. Artigas was proclaimed Protector of this League. Guided by his political ideas (Artiguism), he launched a land reform, dividing land to small farmers. Brazilian province The steady growth of the influence and prestige of the Liga Federal frightened the Portuguese government, which did not want the League's republicanism to spread to the adjoining Portuguese colony of Brazil. In August 1816, forces from Brazil invaded and began the Portuguese conquest of the Banda Oriental with the intention of destroying Artigas and his revolution. The Portuguese forces included a fully armed force of disciplined Portuguese European veterans of the Napoleonic Wars with local Brazilian troops. This army, with more military experience and material superiority, occupied Montevideo on 20 January 1817. In 1820, Artigas's forces were finally defeated in the Battle of Tacuarembó, after which Banda Oriental was incorporated into Brazil as its Cisplatina province. During the War of Independence of Brazil in 1823–1824, another siege of Montevideo occurred. The Thirty-Three On 19 April 1825, with the support of Buenos Aires, the Thirty-Three Orientals, led by Juan Antonio Lavalleja, landed in Cisplatina. They reached Montevideo on 20 May. On 14 June, in La Florida, a provisional government was formed. On 25 August, the newly elected provincial assembly declared the secession of Cisplatina province from Empire of Brazil and allegiance to the United Provinces of the Río de la Plata. In response, Brazil launched the Cisplatine War. This war ended on 27 August 1828 when Treaty of Montevideo was signed.