In the 17th century which duchy was the smallest European country that had colonies in America and Africa?

Like Brandenburg, that had far larger German colonising power before the formation of the German Empire, the Polish-Lithuanian fief of Courland had a European crusading, hence expansionist, past. The colonies were established under Jakob, Duke of Courland and Semigallia, and were indirect colonies of the Polish-Lithuanian Commonwealth. During his reign (1642-1682), the Duchy established trading relations with all of the major European powers. Jakob established one of the largest merchant fleets in Europe, with its main harbours in Windau (today Ventspils), and Libau (today Liepaja). His fleet made voyages to the West Indies as early as 1637 when the settlers established the first colony on Tobago. The first colony was a failure, but it was refounded in 1639.

In 1651 the Duchy established its first colony in Africa, St. Andrews Island at the Gambia River and founded Jacob Fort there. The main export goods included ivory, gold, furs and spices. Soon afterwards, in 1652, Courlanders established another colony, in Tobago in the West Indies. There the main export goods included sugar, tobacco, coffee and spices.

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.