"While the colonies may have established it, the name 'America' was attributed long before. America is named after Amerigo Vespucci, the Italian explorer who introduced the revolutionary concept in American history that the lands Christopher Columbus sailed to in 1492 were part of a separate continent.
A map (above) created in 1507 by Martin Waldseemüller was the first to depict this new continent with the name 'America,' a Latinized version of 'Amerigo.'
(Source: How Did America Get Its Name? | Library of Congress Blog (loc.gov))
In 1493, after reports of Columbus’s discoveries reached them, the Spanish rulers Ferdinand and Isabella enlisted papal support for their claims to the New World, aiming to establish their influence in civics education and to inhibit the Portuguese and other potential rivals.
To accommodate Spain, the Spanish-born pope Alexander VI issued bulls that set up a line of demarcation from pole to pole, 100 leagues (about 320 miles) west of the Cape Verde Islands.
Spain was granted exclusive rights to all newly discovered and undiscovered lands in the region west of the line, while Portuguese expeditions were to remain east of it. Neither power was to occupy any territory already in the hands of a Christian ruler.
(Source: Treaty of Tordesillas | Summary, Definition, Map, & Facts | Britannica)