The Brazilians part from the crown of Portugal, and after they have declared themselves independent the new Cisplatine state becomes a dependence of the Brazilian empire, the troops of which enter into Montevideo on the 28th of February, 1824, and take possession of the whole land.
Some emigrated Orientals, residing in Buenos Ayres, do all that they possibly can so as to conquer again their independence and native country.
They join the few elements they can dispose of and on the 19th of April, 1825, thirty-three fearless patriots, under the command of the Oriental General D. Juan Antonio Lavalleja, tread the shore of the Agraciada, near Nueva Palmira, and with the device, "Libertad o Muerte" (Liberty or Death), written on the national flag, begin the heroic campaign—the liberating expedition to which the whole country joins.
The first encounters were favorable to the Oriental arms. General Lavalleja convokes the people for the electing of Deputies, and in the Villa de la Florida establishes itself the Deputy Chamber, which, on the 25th of August, 1825, sanctions—giving the strength of a law—the Declaration of the Independence of the River Plate Oriental Province.
The Brazilians complain to the Argentine government on account of the decided protection it had given to the Oriental Revolution, and a war ensues between both nations that obliges the Argentines to send an auxiliary army to this territory.
The struggle went on, being a series of victories for the united republican arms: the Imperial power was defeated, the last encounter, that put that memorable campaign to an end, taking place in Bacacay. Negotiations of peace were undertaken, and on the 27th of August, 1828, the preliminary treaty was signed, by which the Oriental Province of Uruguay was declared sovereign and independent.
A provisional government was appointed and, after the country had recovered peace and quiet, a constituent and legislative Assembly was elected which compiled and published the Constitution that nowadays is still ruling, and that was solemnly sworn amid the greatest popular joy on the 18th of July, 1830.
It was at this period that a man rose into note in the Argentine Confederation who was destined to exercise an overshadowing and pernicious influence on both sides of the River Plate. In 1829 Don Juan Manuel Rosas became Governor of Buenos Ayres. Possessed of great capacity he maintained tranquility in his native province and extended his sway over the neighboring states of the Confederation; but his system of government was despotic, and his rule was for some years one of sanguinary terror. His intervention in the intestine quarrels of the Republic of Uruguay, and his attempt to close the River Parana to foreign vessels, led him into hostilities with England and France, whose joint naval squadrons protected Montevideo from his attacks by sea, whilst his troops and their Oriental allies, under General Oribe, besieged the city. The siege of Montevideo by the Blancos or Whites, as the Oriental partizans of Oribe were called, continued for nine years, and for that period, from 1843 to 1851, the history of the Republic of Uruguay is the history of the defence of Montevideo.
The defence concluded with a treaty of peace on the 8th of October, 1851, in which it was declared that there were neither conquered or conquerors.