History is an odd one because the question will always end up being 'where does the history start?' and that's a rabbit hole, and a distraction from the main story - Nolan's mission to stop the plague doesn't really require knowledge of who built what town for example, nor the life history of every NPC he talks to on that quest.

My suggestion for creating a games history is to create a map of the land this story is taking place in. The positions of the settlements can tell a story of that settlement. Is it a settlement in the high reaches of the mountains? Why is that? Were they driven up there, or have they hidden here? Do they practive unnatural magics? How long have they been doing so? Or maybe they just like mining and have found a particularly valuable vein of minerals.

The position of a settlement on the map - where it is, how big it is or how small, suggest stories of their own that you can build on. If you've already built a story, then this becomes a little more difficult - but your map can change to fit your story, and then the history can flow from what your story requires.

I'm no expert but I can share the tips I have gotten an echo what has already been said

yeah keep writing. Try to write every day, anything doesn't matter. Don't feel like you have to stare at a blank page though or feel obligated to write on the same thing (story) until you are 'done' with it. If you feel stuck write something else and go back to it later. The more you write the more confident in your writing you will become. 

Don't throw stuff away, I have hundreds of google doc pages of things I written. non-fiction academic stuff, plain fiction, shorts, Tabletop RPG stuff and game stuff. Even if it's bad it might give you ideas later.

On history I found it really useful to read and learn about world building for tabletop RPGs. Dungeon and Dragons etc. All that advice is easy to translate into writing for video games. 

The above sugfestion from Crashbang is a very useful for me aswell. Start with a place, just a location will give you questions and the answer will generete a history.  
Studying 'real' history can also be really helpful as the same 'rules' apply to your fictional worlds, well mostly... 

My general advise to all creatives/writers would be to read a lot of books, watch a lot of motion pictures and documentaries. Almost all great writers/creatives tend to be knowledgeable in multiple fields because they use it as a source material in their writing or in their creation.

To answer your question more directly, I would suggest that you watch historical documentaries or read historical fiction or anything related to history and use what you've learned as a source of inspiration for your writing.