I often do world building as an exercise for myself. And during these thought exercises, I have created one world that is intended for a book that I want to write in the future.
A rough map of the kingdom of Cordale and the River that flows through it.
The world is set during an age of muskets and colonization, as I have a great interest in that time period and I wanted to explore a world where one nation, called Cordale, thanks to its place in the world, would be the place where every trade ship from a the new world would pass through and how that would affect this country and how it would be viewed by the other powers of the continent.
I also wanted a story of intrigue and duplicity, where the other nations of the world would vie for control of this well placed land and how the people would weather these attempt's.
The way I set about creating both of these situations was by creating a grand river that would flow through most of the continent and place the entrance to this river by Cordale. This would let them control all trade that flows in and out of the continent from the new lands, giving them vast amount of wealth and power, but at the same time invoking jealousy and resent from the rest of the nations of the continent.
To also not make a story that only centered around warfare I could, thanks to the wealth that I had already gave this nation, create a strong military force for Cordale and then explain the other nations reluctance to try and take over the nation with brute force, adding more importance to the intrigue and web weaving and less towards all out warfare.