By the middle of the seventeenth century the United Dutch East India Company (Vereenigde Oost-Indische Compagnie) was the most powerful European institution in Asia. The strength of the company was based on its seapower, but in the territorial sense its activities in Asia had their centre at Batavia, in West Java. From Batavia and the fortress of Malacca (captured from the Portuguese in 1641) the Dutch were able to dominate the Straits of Sunda and Malacca and the seas between Borneo and Sumatra, through which shipping moving from the Indian Ocean into the Eastern Seas, or coming from the Moluccas or the China Sea to the west, had to pass. From this centre they were able to prevent their Portuguese and English rivals from maintaining any significant trading connections with the Indonesian Archipelago, and were themselves well placed to develop a commercial system with factories stretching from Japan to Persia. In the eyes of the company's servants the most important part of this commercial system was the Moluccas, the fabulous ‘spice islands’. The company's hold on the Banda Islands gave it a monopoly of the supply of nutmeg and its by-product mace, whilst Amboina, Ceram and its smaller neighbours in the southern Moluccas provided it with an ample supply of cloves. In the northern Moluccas the Dutch sought by agreements with the Sultan of Ternate, and by punitive military expeditions, to extirpate the cultivation of cloves on islands which they were not themselves exploiting, so as to obtain an effective monopoly of the product.