Over the centuries, the islands were invaded by a succession of diverse groups from the coast of Africa, the Persian Gulf, Indonesia and Madagascar. The culture is mainly of European and Arabic. The earliest inhabitants were probably of Malay-Polynesian origin. Later settlers came from mainland Africa, Madagascar and the Arab world. The Shirazis from Persia became dominant in the 15th-16th century, establishing sultanates in the Comoros linked to their trading settlements in Kilwa (on the coast of present-day Tanzania) and Zanzibar, and dealing in spices and slaves to the Middle East.