Why was Buenos Aires governed from Lima under the Viceroyalty of Peru?

For nearly two centuries, the region of the Río de la Plata, including Buenos Aires, was governed from Lima as part of the Viceroyalty of Peru due to the rigid administrative and commercial structure of the Spanish Empire in the Americas.12

Under this system, the Spanish crown restricted trade to specific authorized ports to maintain strict control over colonial commerce. Within the Viceroyalty of Peru, only Callao—the port near Lima—was permitted to trade with Spanish merchants. This centralization effectively relegated Buenos Aires to a remote backwater, as goods had to be transported over vast distances across the Andes, often taking up to 24 months for a complete exchange.1

This administrative arrangement persisted until 1776, when the Bourbon monarchy established the Viceroyalty of the Río de la Plata with Buenos Aires as its capital. This change was driven by the need to decentralize imperial rule, improve military defenses against Portuguese and British encroachment, and better regulate the growing economic activity in the region.312