Belgrano, in the meanwhile, led an army into Paraguay.  He had confidently expected the adherence of the inhabitants of that country.  These, however, remained loyal to the Crown, and Belgrano, defeated, was obliged to retire.

Operations were now begun against the Spanish troops in Uruguay.  These were conducted by Belgrano, and in a very short time practically the entirety of the province was in the hands of the revolutionists.  Montevideo alone, held by its strong Spanish garrison, continued to resist.  The town was closely invested on its landward side.  Very soon after this, unfavourable news from Peru caused the Argentines to abandon their aggressive attitude; an armistice was declared so far as Montevideo was concerned, and the South American forces retired from Uruguay.

The news from the north, indeed, was sufficiently serious.  After the victory of Suipacha a truce had been agreed upon by Castelli, who was in command of the patriot forces.  This he had observed loyally, but Gueneche, the leader of the Spanish troops, had proved himself less scrupulous.  Without warning, he had attacked the Argentine army at Huaqui, and had obtained a decisive and sanguinary victory, at the end of which the 800 Argentines who survived had been obliged to retire in some confusion to Potosi.

Gueneche now in turn took the aggressive, and, advancing, he crushed the revolution at Cochabamba, and now prepared his forces for serious invasion.  These reverses of fortune were not sufficient to discourage the ardour of the inhabitants of Buenos Aires.  For that the idea of independence had become too strongly engrafted in the young nation; and on February 18, 1812, the blue and white of the Argentine flag was decided upon to the sound of enthusiastic acclamations.

A month later Belgrano took over the command of the army in Peru in order to make a stand against the threatened invasion.  In the first place he found caution necessary.  The Royalists, flushed with victory, had recaptured the towns of Salta and Jujuy, and Belgrano retired for a while in the face of their advances.  The forces under the Spanish General, Tristan, followed him.

This was Belgrano’s opportunity.  Falling upon the Royalist army, he completely defeated it in a battle at Tucuman, and the Spaniards suffered a heavy loss in men and munitions of war.  Belgrano, then in turn advanced and made once again for Salta.  In the neighbourhood of this town the Argentine flags were carried into battle for the first time, and their presence was welcomed as a favourable omen, for the victory remained with the patriot forces.  Belgrano showed himself generous as a victor by liberating the great majority of his prisoners on parole, which, it is regrettable to state, large numbers of the Spaniards broke.

This victory completely changed the situation in the south-east.  The patriots were enabled to resume the aggressive; their armies were sent across once more into Uruguay, and Montevideo was again besieged.