In 1816, a force of 10,000 Portuguese troops invaded the Banda Oriental from Brazil; they took Montevideo in January 1817. After nearly four more years of struggle, the Portuguese Kingdom of Brazil annexed the ''Banda Oriental'' as a province under the name of "Cisplatina". The Brazilian Empire became independent of Portugal in 1822. In response to the annexation, the Thirty-Three Orientals, led by Juan Antonio Lavalleja, declared independence on 25 August 1825 supported by the United Provinces of the Río de la Plata (present-day Argentina). This led to the 500-day-long Cisplatine War. Neither side gained the upper hand and in 1828 the Treaty of Montevideo, fostered by the United Kingdom through the diplomatic efforts of Viscount John Ponsonby, gave birth to Uruguay as an independent state. 25 August is celebrated as Independence Day, a national holiday. The nation's first constitution was adopted on 18 July 1830.