One of the first notable military conflicts taking place in modern Argentina were the British invasions of the Río de la Plata, involving both Buenos Aires and Montevideo (currently part of Uruguay).
For this end he drafted all men capable to bear arms, regardless of their social condition (including slaves), and formed militias to defend the city.
The Regiment of Patricians, led by Cornelio Saavedra, became a strong political force in Buenos Aires, and was instrumental to the failure of the Mutiny of Álzaga and the success of the May Revolution.
However, the status of the different territories that used to belong to the viceroyalty changed many times during the development of the war, as some regions would remain loyal to the former organization, others were captured or recaptured, and later they would divide into several countries.
Belgrano led an ill-fated campaign to Paraguay, and created the Flag of Argentina when preparing the defenses of Rosario against a possible attack from the Banda Oriental (where Montevideo was under siege by Artigas).
Alvear took Montevideo, and San Martín started a military campaign that would span across an important part of the Spanish territories in America.
The Argentine military achieved several victories against Brazil but internal political strife eventually forced them to withdraw and settle for the 1828 Convention of Peace, with the British serving as the intermediary.
The combined forces from the United Kingdom and France seized control of the Paraná River in order to establish trade relationships with Paraguayan ports blocked by Argentina.
[3] The following are key milestones during this period: After the war, the military's role began to shift from the previous appearance as protector of the constitution and of the people against corruption.
The civilian government considered joining the allies, but many officers in the armed forces and ordinary citizens objected due to fears over the spread of communism.