Inter caetera ("Among other ") 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.
It remains unclear to the present whether the pope was issuing a "donation" of sovereignty or a feudal infeodation or investiture. Differing interpretations have been argued since the bull was issued, with some arguing that it was only meant to transform the possession and occupation of land into lawful sovereignty. Others, including the Spanish crown and the conquistadors, interpreted it in the widest possible sense, deducing that it gave Spain full political sovereignty.
The Inter caetera bull and others similar to it made up the Bulls of Donation.
Read more about Inter Caetera: Background, Provisions, Modern Protests By Indigenous Peoples