The State of Buenos Aires was a secessionist republic resulting from the overthrow of the Argentine Confederation government in the Province of Buenos Aires on September 11, 1852. The State of Buenos Aires was never recognized by the Confederation; it remained, however, independent under its own government and constitution. Buenos Aires rejoined the Argentine Confederation after the former's victory at the Battle of Pavón in 1861.

The Argentine Confederation was the last predecessor state of modern Argentina; its name is still one of the official names of the country according to the Argentine Constitution, Article 35. It was the name of the country from 1831 to 1852, when the provinces were organized as a confederation without a head of state. The governor of Buenos Aires Province managed foreign relations during this time. Under his rule, the Argentine Confederation engaged in conflicts with Brazil, Bolivia, Uruguay, France and the United Kingdom, as well as other Argentine factions during the Argentine Civil Wars.