When the English invaded Buenos Aires City in 1806, Belgrano, an honorary captain, found himself commanding troops despite the fact that he had no military experience. But he was instrumental in organizing forces which later expelled the invaders. Belgrano and other criollos consequently acquired a sense of their own importance and power.
After 1807 Belgrano became increasingly critical of the Spanish system and found others who agreed with him. A secret society of revolutionists was organized with Belgrano reportedly a member. His caustic comments on Spanish regulations were disseminated through the Correo de comercio, a newspaper he helped found in March 1810. In April he resigned from the Consulado, pleading illness. But in May, when news reached Buenos Aires that the Spanish junta established in 1808 had been disbanded, Belgrano and his compatriots quickly advocated the creation of a local junta. On May 25, 1810, when the junta was organized, Belgrano was elected a member.
The initial concern of the junta was defending Buenos Aires while securing the support of the surrounding provincial cities. Because of Belgrano's military record and the fact that other criollos had even less experience, he was named a general and ordered to assemble an army. In September 1810 the ill-equipped and poorly trained force made an unsuccessful foray into Paraguay. Belgrano was blamed for the disaster, but after an investigation he was cleared in August 1811.
He was subsequently appointed commander of an army defending the northwestern district from a Spanish invasion from Upper Peru (modern Bolivia). As a standard for the troops, he designed a banner which later became the national flag. With the outbreak of hostilities Belgrano was forced to retreat, but at the battle of Tucumán, on Sept. 24, 1812, he disobeyed orders, stood, fought, and checked further Spanish advances. Buenos Aires was spared, and his disobedience overlooked. Belgrano followed up the victory with an advance into the northwest. At Salta, on Feb. 20, 1813, he gained another stunning victory over the royalists, and the way was open for an invasion of Upper Peru. However, his armies were forced to withdraw after suffering a series of setbacks.
Belgrano, again in disfavor, was sent on a diplomatic mission to Europe to secure British recognition for the Buenos Aires government and to search for a monarch. He returned in February 1816, unsuccessful in obtaining either. Back in favor, he resumed his military career. At the Congress of Tucumán, Belgrano was an outspoken advocate for a declaration of independence and the establishment of a monarchy with a descendant of the Inca on the throne. Reappointed to his old command as chief of the army of the North, for the next 3 years he fought not only Spanish regulars but armies of provincial caudillos as well. The constant traveling and campaigning exhausted him. He returned to Buenos Aires in March 1820 and died on June 20.