It is important that you mention purpose for the sake of my answer, the approach would be very different if someone were just building a world for the sake of building one.
This is a multistage, repeating process for me but this is how I generally approach history.
Step 1: Define the world/setting you want.
- Define what you want to happen. In my case that is the story I am writing. Basically you are saying you want a world that looks like X.
- From there you will need to decide at least a few major events that have happened in the past. A good place to start is to look at sources of conflict, be they racial or political or personal, those conflicts have a source somewhere in history.
- Here are a few examples: Dynasties falling, a bloody major war (WWII scope), major social or societal changes (signing of the Magna Carta for example), the founding of a group that plays a role in the outcome of history, or maybe a terrible massacre.
- Integrate your story points and the plot items you have and make sure they blend together
Note that in the process of integrating things may change, be added or in some cases completely removed.
At this point you have a framework for history, this should most definitely be a very very high level view. If you are having to de-conflict plot points you are too far into the details at this point and it is important to the next step that you don't get to far into the weeds.
Step 2: Create a map Map creation itself isn't all that hard, draw a landmass, add some mountains, add some rivers, maybe some major forests and other biomes, viola! You have a map. This step is significantly more complex. This series will help with the first part: Creating a realistic world map - Landmass formation
- Do what I mentioned above...draw it out. Do not add cities, roads, ports, holy sites, historic markers, none of that. If its not geography make it wait. Note, the more preconceptions or ideas you start with at the beginning of the process the more complicated it will be...I had several plot points that included specific locations and every time I tried to make a map to fit...it didn't work and I started over. I ended up changing the story to fit the map.
- Place nations. Mountains and bodies of water make great natural lines of demarcation obviously but its always a decent idea to create some borders that are not based on geography, perhaps based on a treaty.
- Place cities and castles and other key points of interest. Add roads, major ports (keeping climate in mind. cold = bad for shipping for example) and trade routes. Cities tend to form near intersections be that of roads or rivers or some of each. These should be helpful: A realistic road network AND How can I ensure my cities don't all look the same?
Step 3: Put them together You now have a map as well as the key setting items you want in your world. Start looking at how and where things come together. Was there a great empire? Is there a place where two countries are in conflict. Has language been imported by invaders in the past (mixes naming conventions for cites and such)? Keep a few things in mind when doing this:
- Biomes: They will impact what sort or natural resources each area has, it will impact population density (more food, more people), what kind of wildlife there is (could have religious implications. All these things can lead to conflict (or cooperation).
- Nation aspects: Defining how nations behave, what kind of systems (democracy, dicatatorship etc etc etc) they have, religious preference, what they trade, what they have vs need, racial makeup...all that.
The point in putting them together is that if you keep asking what happens here, or what does this nation want, etc etc etc eventually the history begins to write itself, and best yet it can evolve within the system you create as you are writing. If you avoid creating more than you need at the time (and are willing to massage the map or other things that have been decided) you can work in other things you need later. For example when you are writing you think...oh man I wish there was a nomadic tribe my character could meet. Oh wait! Look there on the map! Its a section that is not affiliated with a country. Bam, good to go.
As you dig into this you will end up with excellent, consistent and detailed information. As an example I started with a city state in mind as the setting for the start of my book. It went from being a mountain mining city in my head to becoming a desert port when I finished my map. It also happens to be the continental headquarters to my assassin's guild. Another city (which I only had vague ideas about) ended up (due to its geographic location) being the center of the world's major religion, which in turn impacts how it interacts with its neighbors, as well as its economy etc etc etc.
TL;DR You are creating a system, think of it as a video game engine if that helps, its a network of items (places, people, landmarks, etc etc) each with its own stats and back story. If you develop the framework you will be able to ask a question about what would happen if fill in the blank in my world. The framework should allow you to answer that question and frankly, in the end, it helps you write the story too. And don't fall in love with ideas (its a hard thing to do), sometimes as cool as they may seem they just don't fit.