Causes
The 1810 May Revolution followed the deposition of the Spanish king Ferdinand VIII by the Napoleonic French. The revolution ended the authority of the Viceroy Cisneros and replaced it with the Primera Junta.
When the Spanish monarchy resumed its functions in 1819, Spain was determined to recover control over its colonies in the Americas. Moreover, the royalists from Peru had been victorious at the battles of Sipe-Sipe, Huaqui, Vilcapugio and Ayohuma, in Upper Peru, and seriously threatened the United Provinces from the north.
On April 15, 1815, a revolution ended the mandate of Carlos María de Alvear as Supreme Director and demanded that a General Congress be summoned. Delegate deputies, each representing 14,000 inhabitants, were sent from all the United Provinces of the Río de la Plata to the sessions, which started on March 24, 1816. However, the Federal League Provinces did not send delegates: the Argentine littoral Provinces (Santa Fé, Entre Ríos, Corrientes and Misiones), and the Eastern Province (modern-day Uruguay).
Read more about this topic: Argentine Declaration Of Independence