History of Madagascar
By the 15th century, Europeans had wrested control of the spice trade from the Muslims. They did this by bypassing the Middle East and sending their cargo-ships around the Cape of Good Hope to India. The Portuguese mariner Diogo Dias became the first European to set foot on Madagascar when his ship, bound for India, blew off course in 1500. In the ensuing two-hundred years, the English and French tried (and failed) to establish settlements on the island.
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.