The first thing I want to sort out is the basic layout of the world including continents and the countries on them and then hash out some info on the current state of the world. I have always enjoyed the idea of tidally locked planets but they come with multiple problems with the situation of the habitable zone. These are solved by instead setting everything on a moon of a gas giant. With a little fudging of the physics and making sure the inhabited side is the outside facing one, I can have my cool tidally locked planet and the edges of the continent will have a gas giant on the horizon if we visit there.
On the inside face of the moon will be more land but due to the nature of having an eclipse every day and the land being very mountainous, it will be too treacherous to sail to or live on which keeps all the action on the main piece of land. I realise this makes my world very similar in design to the one in Dishonored but by having it on a moon, my continent size is reduced and I can have the war encompass all living people on the world.
Rather than design the actual map myself, I went on the hunt for map generators I could use to produce a map for me that I could further customise as needed. This also meant I could cut down on research time, leaving me to worry more about how to lay out my countries and which towns/cities would be important than how the world is actually laid out.
After a lot of looking and testing a few out, I settle on using one by a person called Azgaar on github whose generator can be found here. I played around a lot with generating height maps and moving the country borders around until I was happy with what I had. The current layout is almost exactly what I wanted to help set the current state of affairs. I still need to go in and start changing the names of things but the land mass will very likely not change from here on out.
The two countries are as different as can be. The northern country of Ezuratu is mostly a monoculture very similar to Victorian Britain apart from the western part which is more akin to an Eastern Europe civilisation with a very militaristic outlook. The southern country of Teirith is a collection of smaller cultures that is held together by a senate and ruled by monarch who is voted in by the Senate and can be removed any time by a 2/3 vote in the Senate or abdication.
At the time of the game, the current ruler of Ezuratu has presided over a recent industrial revolution sparked by the discovery that a mineral unique to this world can be burned for large amounts of energy if prepared properly. The southern cultures have all found various uses for the same mineral but nothing on the scale of the Ezuratians.
The Governor of Ezuratu started a war to capture the mines under the control of Teirith and to unite the continent under one ruler. This was several years ago and after a few bloody battle the war has mostly ground to a halt in trench warfare along a front that stretches from coast to coast just south of the border between the two countries. Only the mountain in the middle has prevented the entire front line from being inside Teirith and it's capital is dangerously close to the trenches.
All of this is a good starting point from which I can flesh out characters in the world, exactly what the southern cultures are like and the fashions and items of each place. This is now where I start my research in full to get a decent foundation on what my designs will be and how everything in the world will look.