An understanding was entered into by Buenos Aires Governor Juan Manuel de Rosas and other Federalist leaders out of need and a shared enmity toward the still vigorous Unitarian Party.

The central figure in the overthrow of Rosas, Entre Ríos Governor Justo José de Urquiza, was granted the power of a head of state by the Palermo Protocols of 6 April 1852.

[2] The prospect of having the Argentine Congress headquartered in Santa Fe proved especially objectionable, and Urquiza's 12 June appointment of former President Vicente López y Planes failed to turn public opinion in Buenos Aires.

The siege continued through June 1853, and Urquiza commissioned a naval flotilla to blockade Buenos Aires (whose chief source of revenue was duty collected at the port).

Article 1 said "Buenos Aires is a State that, until it delegates its sovereignty to a federal government and does so expressly, freely exercises its sovereignty internally and with respect to the outside world" (Buenos Aires es un Estado con el libre ejercicio de su soberanía interior y esterior, miéntras no la delegue expresamente en un gobierno federal).

[4]: xxviii The territory of the State of Buenos Aires was defined very vaguely in Article 2, but extended to the foothills of the Andes and included Martín García Island.

Then in 1854 the State Department accredited James A. Peden of Florida as minister resident to Buenos Aires: an American diplomat of such seniority had not been sent to the Río de la Plata since 1823.

For example, on 8 January 1855 both parties signed a convention dealing with such matters as military cooperation against Indian raids, the extradition of fugitive criminals, that the ships of both polities must fly the Argentine flag, and customs and postal co-operation.

The 1854 constitution, drafted by Dalmacio Vélez Sársfield, asserted the sovereignty of Buenos Aires, including its right to engage in its own diplomatic relations, as well as a bicameral legislature and freedom of worship.

Ordered by Congress in Santa Fe to subjugate Buenos Aires separatists by force, Urquiza instead invited the defeated to join negotiations, though he obtained Alsina's resignation.

These talks resulted in the Pact of San José de Flores of 11 November 1859, which provided for a number of constitutional amendments and led to other concessions, including an extension on the province's customs house concession and measures benefiting the Bank of the Province of Buenos Aires, whose currency was authorized for use as legal tender at the port (thereby controlling much of the nation's foreign trade).

Mitre, who despite victory reaffirmed his commitment to the 1860 constitutional amendments, was elected the republic's first president on 4 September 1862, and remained Governor of Buenos Aires as caretaker until his 12 October 1862, inaugural.