Lines dividing the non-Christian world between Castile (modern Spain) and Portugal: the 1494 Tordesillas meridian (purple) and the 1529 Zaragoza antimeridian (green)
On July 2, 1494, Spain ratified the Treaty of Tordesillas, which was signed on June 7 before, by Spain and Portugal, to divide the New World, with the intervention of Pope Alexander VI, as conciliator and head of the Church.
The signatories were representatives of the Catholic Church, monarchs Ferdinand of Aragon and Isabella of Castile, by Spain; and João II of Portugal. The planet was divided into two hemispheres by an imaginary line 370 leagues west of the Cape Verde Islands, off the coast of Senegal, Africa.
West and the recently reached Americas, Tordesillas line depicted - Cantino planisphere detail
The rhumb-line construction scheme and geographic lines in the Cantino planisphere or world map. Adapted from Gaspar (2012)
The land to the west of this meridian belonged to the Spanish crown, and the eastern to the Portuguese. As the eastern outgoing territory of South America was within the Portuguese area, this country begun the colonization of Brazil in 1500.
Catholic priests believed they had a divine right to guide, not just to their Christian sheep but also the infidels and savages, by the grace of God.