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ポルトガルはキリスト教・イスラム教の戦争が激化した時期にモロッコの沿岸部を領地にし
全般的に不調だったオスマン・トルコとの戦争を有利にすることを目的とした

この沿岸部ではイスラム教徒の奴隷貿易が大きな利益を出しており、大航海時代のポルトガルが
奴隷貿易を高利の商売として認識することになる継続した

https://en.wikipedia.org/wiki/Romanus_Pontifex
https://upload.wikimedia.org/wikipedia/commons/0/0f/Portuguese_Morocco.PNG
Portuguese ventures were intended to compete with the Muslim trans-Sahara caravans, which played a key
role in the highly profitable Muslim slave trade and also held a monopoly on West African gold and ivory.[15]

The Portuguese claimed territorial rights along the African coast by virtue of having invested time and treasure
in discovering it; the Castilian claim was based on their being the heirs of their Visigoth ancestors. In 1454 a
fleet of caravels from Seville and Cadiz traded along the African coast and upon their return, were intercepted
by a Portuguese squadron. Enrique IV of Castile threatened war. Afonso V appealed to the Pope for moral support
of Portugal's right to a monopoly of trade in lands she discovered.[16]