I really liked it, it’s a very interesting concept.
Just a small suggestion: shouldn’t the game be able to automatically find the fastest route? For example, in this image:

When I try to go to the city in the lower-left corner, the most logical thing would be for the caravan to follow the road (because it is faster), but instead it takes a less efficient path. Maybe the pathfinding system could take roads or terrain costs into account to determine the optimal route.