. . . the Pope divided the world in two, roughly speaking, in the bull Inter Caetera.
Inter caetera ("Among other [works]") was a papal bull issued by Pope Alexander VI on 4 May 1493, which granted to Spain (the Crowns of Castile and Aragon) all lands to the "west and south" of a pole-to-pole line 100 leagues west and south of any of the islands of the Azores or the Cape Verde islands.
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Columbus's arrival in supposedly Asiatic lands in the western Atlantic Ocean in 1492 threatened the unstable relations between Portugal and Spain. With word that King John [of Portugal] was preparing a fleet to sail to the west, the King and Queen of Spain initiated diplomatic discussions over the rights to possess and govern the newly found lands. Spanish and Portuguese delegates met and debated from April to November 1493, without reaching an agreement.
Columbus was still in Lisbon when he sent a report of his success to the Spanish monarchs. On 11 April, the Spanish ambassador conveyed the news to Pope Alexander VI, a Spaniard native of Valencia, and urged him to issue a new bull favorable to Spain.
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In response to Portugal's discovery of the Spice Islands in 1512, the Spanish put forward the idea, in 1518, that Pope Alexander had divided the world into two halves. By this time, however, other European powers had overwhelmingly rejected the notion that the Pope had the right to convey sovereignty of regions as vast as the New World.
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Various groups representing indigenous peoples of the Americas have organised protests and raised petitions seeking the repeal of the papal bull Inter caetera, and to remind Catholic leaders of the record of conquest, disease and slavery in the Americas, sometimes justified in the name of Christianity, which has a devastating effect on their cultures today.
There's more at the link.
Certainly, the Spanish colonization of South America was a human tragedy of immense proportions. I doubt whether the hapless indigenous peoples, if they had been able to record their opinions of the Pope's grandiloquent gesture, would have approved.