"To invade, search out, capture, vanquish, and subdue all Saracens and pagans whatsoever, and other enemies of Christ wheresoever placed, and the kingdoms, dukedoms, principalities, dominions, possessions, and all movable and immovable goods whatsoever held and possessed by them and to reduce their persons to perpetual slavery."
From the Romanis Pontifex by Pope Nicholas V to King Afonso V of Portugal, 1455
In the 1400s, at the beginning of the period of European exploration and expansion known as the "Age of Discovery," decrees issued by Roman Catholic popes outlined the idea that Christian monarchs had God-given rights to claim non-Christian lands and assert authority over the lands' inhabitants. Indigenous peoples were often expected to convert to Christianity or be enslaved, displaced, or killed. These beliefs were used by monarchs in Spain, Portugal, England, France, and Holland to justify world exploration and colonization.
This idea surfaced again in 1823, when Chief Justice John Marshall of the U.S. Supreme Court explained that colonial powers claimed "newly discovered" lands during the Age of Discovery. It reaffirmed that title to those lands belonged to the government whose subjects discovered the "new" territory. The doctrine ignored the occupation of the lands by indigenous peoples, who were considered inferior to the colonizing nations.
The doctrine has been cited as recently as 2005 in the decision City of Sherrill
v. Oneida Indian Nation of New York.