Unitarian Party in the context of Federalist Party (Argentina)

The Uruguayan War (10 August 1864 – 20 February 1865) was fought between Uruguay's governing Blanco Party and an alliance consisting of the Empire of Brazil and the Uruguayan Colorado Party, covertly supported by Argentina. Since its independence, Uruguay had been ravaged by intermittent struggles between the Colorado and Blanco factions, each attempting to seize and maintain power in turn. The Colorado leader Venancio Flores launched the Liberating Crusade in 1863, an insurrection aimed at toppling Bernardo Berro, who presided over a Colorado–Blanco coalition (fusionist) government. Flores was aided by Argentina, whose president Bartolomé Mitre provided him with supplies, Argentine volunteers and river transport for troops.

The fusionism movement collapsed as the Colorados abandoned the coalition to join Flores' ranks. The Uruguayan Civil War quickly escalated, developing into a crisis of international scope that destabilized the entire region. Even before the Colorado rebellion, the Blancos within fusionism had sought an alliance with Paraguayan dictator Francisco Solano López. Berro's now purely Blanco government also received support from Argentine federalists, who opposed Mitre and his Unitarians. The situation deteriorated as the Empire of Brazil was drawn into the conflict. Almost one fifth of the Uruguayan population were considered Brazilian. Some joined Flores' rebellion, spurred by discontent with Blanco government policies that they regarded as harmful to their interests. Brazil eventually decided to intervene in the Uruguayan affair to reestablish the security of its southern frontiers and its regional ascendancy.

The current Constitution of the Argentine Republic dates back from 1853. The Argentine Constitution of 1853 was approved in 1853 by almost all of the provincial governments with the exception of Buenos Aires Province, which remained separate from the Argentine Confederation until 1859. After several modifications to the original constitution and the return of power to Buenos Aires' Unitarian Party, it was sanctioned on May 1, 1853, by the Constitutional Convention that had gathered in Santa Fe. The document was promulgated by the provisional director of the national executive government, Justo José de Urquiza, who was a member of the Federalist Party. Following the short-lived constitutions of 1819 and 1826, it was the third constitution in the history of the country.

Despite several reforms of varying importance, the 1853 constitution formed the basis of the current Argentine juridical system. It was closely inspired by the juridical and political doctrines of the United States Constitution. It established, for example, a Republican division of powers, a high level of independence for provinces, and a federal power controlled by a strong executive government that was limited by a bicameral national congress to balance the population's representation. It also drew from the previous constitutions, as well as the pioneering works of the jurist Juan Bautista Alberdi.

The Tarija War (Spanish: Guerra por Tarija), also known as the War between Argentina and the Peru–Bolivian Confederation (Spanish: Guerra entre Argentina y la Confederación Perú-Boliviana), was an armed conflict that occurred between 1837 and 1839. Because it happened while the Peru–Bolivian Confederation was engaged in a parallel war against the Republic of Chile during the so-called War of the Confederation, both conflicts are often confused. The Tarija War began on May 19, 1837, when Juan Manuel de Rosas, who was in charge of managing foreign relations for the Argentine Confederation and was governor of the Province of Buenos Aires, declared war directly on President Andres de Santa Cruz because of the Tarija Question and Confederation's support for the Unitarian Party.

The operations began in August 1837, when Bolivian Confederate troops invaded most of the Province of Jujuy, the Puna de Jujuy, and the north of the Province of Salta. The war continued with a series of combats and skirmishes between both forces, all of them without conclusive results. In May and June 1838, the Confederate army defeated Rosas's troops in a series of engagements, the most important of which was the Battle of Montenegro, which in practice led to Argentina's withdrawal from the war, which from then on had a defensive posture being maintained, but the state of war continued until the victory of the Chilean-Peruvian restorative army at the Battle of Yungay, which put an end to the Peru-Bolivian Confederation.