However, they also tried to lessen the role of independent trading ports in the archipelago by making them part of the VOC trading system. In many cases, they tried to impose treaties guaranteeing their monopoly either in production, trade, or in import markets at fixed prices (Cowan, 1968). 26 The role of Aceh as a trading power in the Straits of Malacca in the 17th century was also discouraged by the VOC. Dutch sea power eventually dominated the key trade routes of the archipelago. The Dutch could control shipping traffic on the Straits of Malacca and Sunda, since they already had occupied Batavia (for the Straits of Sunda) and Malacca (for the Straits of Malacca) as the main gates to Europe, as well as the Maluku Islands as the main producers of spices.