The treaty of Torresillas.

When Colombus discovered America, the Catholic Monarchs asked the Pope for permission to rule and evangelise the new territory.
Portugal also wanted to control the sea and the territory explored by its navigators. To avoid conflict between the two nations, the Treaty of Torresillas was signed in 1494.
The Treaty of Torresillas divided the newly discovered territories between Spain and Portugal along a meridian 370 degrees west of the Cape Verde Islands. All territories west of the line belonged to Castile, and all territories east of the line belonged to Portugal.