"authorized by papal proclamations dating from the time of the Crusades [which] allowed the outright confiscation of the property and sovereign rights of heathens". The Council disagreed, stating that non-Christians had claims to rights of sovereignty and property under natural law. However, the Council upheld that conquests could "legally" occur if non-Christians refused to comply with Christianization and natural law. This effectively meant that peoples who were not considered "civilized" by European standards or otherwise refused to assimilate under Christian authority were subject to war and forced assimilation: "Christians simply refused to recognize the right of non-Christians to remain free of Christian dominion." Christian Europeans had already begun invading and colonizing lands outside of Europe before the Council of Constance, demonstrating how the doctrine was applied to non-Christian Indigenous peoples outside Europe. In the 14th and 15th centuries, the Indigenous peoples of the Canary Islands, known as Guanches, became the subject of some colonizers' attention. The Guanches had remained undisturbed and relatively "forgotten" by Europeans until Portugal began surveying the island for potential settlement in 1341. In 1344 the Papacy issued a bull which assigned the islands to Castile, a kingdom in Spain. In 1402, the Spanish began efforts to invade and colonize the islands. In 1436 Pope Eugenius IV issued a new papal edict, Romanus Pontifex, which authorized Portugal to convert Indigenous peoples to Christianity and to control the Canary Islands on behalf of the pope. The Guanches resisted European invasion until the surrender of the Guanche kings of Tenerife to Spain in 1496. The invaders brought destruction and diseases to the Guanche people, whose identity and culture disappeared as a result. As Portugal expanded southward into North Africa in the 15th century, subsequent popes added new edicts which extended Portuguese authority over Indigenous peoples. In 1455, Pope Nicholas V re-issued the Romanus Pontifex with more direct language, authorizing Portugal "to invade, search out, capture, vanquish, and subdue all Saracens and pagans" as well as allowing non-Christians to be placed in slavery and have their property stolen. As stated by Robert J. Miller, Jacinta Ruru, Larissa Behrendt, and Tracey Lindberg, the doctrine developed over time "to justify the domination of non-Christian, non-European peoples and the confiscations of their lands and rights". According to Miller, Ruru, Behrendt, and Lindberg, as Portugal had been granted "permissions" by the papacy to expand in Africa, Spain was moved to expand westward across the