However, during this time, the Duchy of Courland remained an object of interest for both Sweden and the Polish–Lithuanian Commonwealth. In 1655 the Swedish army entered the territory of the Duchy, starting the Swedish–Polish war (1655–60). The Swedish army captured Duke Jacob (1658–60). During this period, the Dutch took over both of Courland's colonies that lacked supplies and manpower, and the merchant fleet and factories suffered destruction. This war ended with the peace Treaty of Oliwa (1660). Courland regained Tobago on the basis of the treaty and held it until 1689. Duke Jacob set about restoring the fleet and factories, but the Duchy of Courland never again reached its pre-war level of prosperity.