Duke Jacob of Courland was a ruler of the Duchy of Courland and Zemgale for 40 years (1642-1682).  There were great changes during his rule, with the ship building industry developing rapidly, the first factories appearing, and agricultural output improving.  The duke had a large fleet that brought grain, meat, butter, wool, timber and all that was manufactured at baronial estates in Zemgale and Courland to Western Europe.  The fleet was so big and strong that its ships sailed not just to Europe, but also all the way to Tobago and Gambia, where colonies were established to bring sugar, coffee and spices to Europe.

The duchy built ships, manufactured paper and saltpetre and wove textiles, brocade and tapestries.  Iron manufacturing was highly developed, and ore was imported from Sweden.  This made it possible to forge nails, anchors, bells, cannons and other firearms.  The duchy produced vodka, vinegar and gunpowder for which there was great demand in Europe, because there were attacks and defences that required it.  As much as 25 tonnes of gunpowder were produced each year.  One of the gunpowder towers is still in Kandava, though it has been rebuilt many times.  The duchy manufactured sails and ropes, as well as hemp ropes.  It was said that the fleet of the Queen of England would not have existed without those ropes.  The duke also thought about selection of grain, bred livestock, improved land with land reclamation and tried to expand output from his fields.

Jacob did not manage to do everything that he wanted to do.  A canal to avoid the Venta rapids was not finished, and plans such as the colonisation of Australia were not finished.  Yet the era of Duke Jacob was a period of great change in the territory of Latvia, and it has not gone unnoticed that the great achievements of the duke occurred on a small plot of European land.  That proves that wise management can ensure lots of progress.