It attained its climax of power in the time of Sultan Iskandar Muda (1607-1636), under whom the subject coast extended from Aru opposite Malacca round by the north to Benkulen on the west coast, a sea-board of not less than 110o miles; and besides this, the king's supremacy was owned by the large island of Nias, and by the continental Malay states of Johor, Pahang, Kedah and Perak.
The natives, about 3000 in number, are of Malayan or pre-Malayan stock, akin to those of the island of Nias to the north-west.
To the government of the west Coast belong the following islands: Simalu; Banyak Islands, a small limestone group, well wooded and sparsely peopled; Nias; Batu Islands (Pulu Pini, Tana Masa, Tana Bala, &c.);; Mentawi and Pegeh or Nassau Islands.
In 1863 there was an expedition against Nias, and in 1865 another against Asahan and Serdang (east coast).
Unlike Java, Sumatra has a series of considerable islands (Nias Islands, Mentawi Islands, &c.) arranged like outworks in front of the west coast, which faces the open Indian Ocean.