The scene of slaughter was extended to the Banda Oriental by the attempt of Oribe, with the support of Rosas, and of Justo Jose de Urquiza, governor of Entre Rios, to establish himself as president of that republic (see Uruguay), where the existing government was hostile to Rosas and sheltered all political refugees from the country under his despotic rule.
The downfall of Rosas was at last brought about by the instrumentality of Justo Jose de Urquiza, who as governor of Entre Rios, had for many years been one of his strongest supporters.
The first efforts of Urquiza to rouse the country against the oppressor were unsuccessful, but in 1851 he concluded an alliance with Brazil, to which Uruguay afterwards adhered.
A provisional government was formed under Urquiza, and the Brazilian and Uruguayan troops withdrew.
A constituent congress, in which each province had equal representation, was duly gress had (May 1, 1853) appointed Urquiza president of the confederation, and he established the seat of government at Parana.
The army of the portent's, commanded by Colonel Bartolome Mitre, was defeated at Cepeda by the confederate forces under Urquiza, and Buenos Aires agreed to re-enter the confederation (November 11, 1859).
Urquiza at this juncture resigned the presidency, and Doctor Santiago Derqui was elected president of the fourteen provinces with the seat of government at Parana; while Urquiza became once more governor of Entre Rios, and Mitre was appointed governor of Buenos Aires.
Causes of friction still remained, but they did not develop into open quarrels, for Mitre was content to leave Urquiza in his province of Entre Rios, and the other administrators (caudillos) in their several governments, a large measure of autonomy, trusting that the position and growing commercial importance of Buenos Aires would inevitably tend to make the federal capital the real centre of power of the republic. In 1865 the Argentines were forced into war with Paraguay through the overbearing attitude of the president Francisco Solano Lopez.
The rebels had hoped for assistance from Urquiza, but the powerful governor of Entre Rios maintained the peace in his province, which under his firm and beneficent rule had greatly prospered, and the revolutionary movement was quickly subdued.
Urquiza was assassinated, and the provincial legislature, through fear, at once proclaimed Lopez Jordan governor.
But Urquiza was a man of different temperament from Rosas, and when he found that Buenos Aires refused to submit to his authority, he declined to use force.
The con Mitre parties, under Generals Mitre and Urquiza respectively,.
An army of Correntine, Uruguayan and Brazilian troops, under General Urquiza, assisted by a Brazilian naval squadron, advanced on Buenos Aires, completely routed the forces of Rosas, and crushed for ever the power of that dictator.