How are prince Henry the navigator and vasco de gama related.

Prince Henry of Portugal – also called Prince Henry the Navigator – began Portugal’s great age of exploration. From about 1419 until his death in 1460, he sent several sailing expeditions down the coast of Africa.4 In 1481, King John II of Portugal began sending expeditions to find a sea route around the southern shores of Africa. Many explorers made several attempts. It was Bartolomeu Dias who was the first to round Africa and make it to the Indian Ocean in 1488. But he was forced to head back to Portugal before he could make it to India.

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what the first or next guys says

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).