The Treaty of Tordesillas, signed in 1494, divided newly discovered lands beyond Europe between Spain and Portugal, using a north-south meridian 370 leagues west of the Cape Verde Islands. This agreement effectively split the South American continent into two spheres: Spain controlled most territory to the west of the line, while Portugal claimed land to the east, setting the stage for subsequent colonization and exploitation by these European powers.

This division significantly influenced language dominance in the region. Portuguese dominance in the area now known as Brazil emerged from strong Portuguese presence, leading to widespread adoption of the language. Conversely, Spanish explorers and colonizers claimed much of the remaining South American territories, spreading the Spanish language.

Over time, this colonial rule solidified Portuguese in Brazil and Spanish as the dominant language elsewhere in South America, deeply influencing the cultures and societies of these regions.