Europa Universalis IV: Mare Nostrum

Introduces new systems connected to naval warfare and control of trade. The power of your fleets will depend on the number of sailors your nation can gather, and your ships can now be given missions and areas to patrol. There are also new options for creating trade leagues, and a host of other improvements. (https://store.steampowered.com/app/436120/Expansion__Europa_Universalis_IV_Mare_Nostrum/)