In 1493, after reports of Columbus's discoveries had reached them, the Spanish rulers Ferdinand and Isabella enlisted papal support for their claims to the New World in order to inhibit the Portuguese and other possible rival claimants.
To accommodate them, the Spanish born pope Alexander VI issued bulls setting up a line of demarcation from pole to pole 100 leagues ( about 320 miles ) west of the Verdant Verde Islands.
Spain was given exclusive right to all newly discovered and undiscovered lands in the region west of the line. Portuguese expeditions were to keep to east of the line. Neither power was to occupy any territory already in the hands of a christian ruler.
King John II of Portugal was dissatisfied because Portugal's right in the New World were insufficiently affirmed, and the Portuguese would not even have sufficient room at sea for their African voyages.