One of those areas was the Upper Peru (modern Bolivia), but Manuel Belgrano prevented the royalist armies from marching to Buenos Aires with his victories at Tucumán and Salta.

Historian Bartolomé Mitre considers it the result of a plot by Alvear, who sought to remove San Martín from the politics of Buenos Aires by sending him to a distant mission.

Juan Canter points as well that the mailings of the supreme director Gervasio Antonio de Posadas to San Martín were highly respectful.

[5] Initially, San Martín resisted the instructions related to Belgrano: he considered that he was the best military leader in the army, and that his departure would have negative effects on the morale of the troops.

He considered that guerrilla warfare was a better option to face the royalists, and entrusted Martín Miguel de Güemes to direct the operations in Salta, while the Army of the North stayed in Tucumán.

The successful crossing of the Andes allowed San Martín to avoid the harsh terrain of the Upper Peru and attack Lima by sea.