European exploration of Africa
One of the ships under command of Diogo Dias arrived at a coast that was not in East Africa. Two years later, a chart already showed an elongated island east of Africa that bore the name Madagascar. But only a century later, between 1613 and 1619, did the Portuguese explore the island in detail. They signed treaties with local chieftains and sent the first missionaries, who found it impossible to make locals believe in Hell, and were eventually expelled.
History of Madagascar
As for the cause of the coming of these Austronesians, the history of the Indian Ocean from the early first millennium AD is still poorly understood. One can only assume that the island of Madagascar played an important role in trade, particularly that of spice trade (especially the cinnamon) and timber between Southeast Asia and Middle East, directly or through the African coast and Madagascar.