The Duchy of Courland was the smallest nation to colonize the Americas with a colony on the island of Tobago from 1654 to 1659, and intermittently from 1660 to 1689. Courland had a population of only 200,000 and was itself a vassal of the Polish-Lithuanian Commonwealth at that time. Under Duke Jacob Kettler, a Baltic German, it established one of the largest merchant fleets in Europe. During his travels to Western Europe, Jacob became the eager proponent of mercantile ideas. Metalworking and shipbuilding became much more developed. Trading relations were established not only with nearby countries, but also with Great Britain, France, the Netherlands, Portugal and others. Kettler established one of the largest merchant fleets in Europe, with its main harbours in Windau (today's Ventspils), and Libau (today's Liep ja).