As an extension to my previous question, how do the creators of fantasy worlds like Bethesda for Elder Scrolls, Tolkien etc. actually make their worlds? I can't imagine that the Bethesda developers have a vast knowledge of politics and history, and Tolkien was only one man.
They worked on it piece and piece. You can't make entire worlds in a day, and it's an always on-going process. I am almost certain that Tolkien was still working on his world even when he died.
Now, you don't need a vast knowledge of everything. You just need to know some basics. In fact, you only need to know as much as you want to know, depending on how realistic you want your world to be. Some conworlders take great pains to make sure their planets, for instance, have realistic climates and geology (so for instance deserts and jungles will be exactly where they should be), and this, of course, requires a bit of knowledge about earth science (though not as much as you might think). Yet you don't need that. You can just have the world's geography be outrageously funky. It's not necessary.
For me, when I conworld, I do it piece by piece. I add a little here, a little there; sometimes I have to make modifications (major or minor) to my previous work. Sometimes I have to scrap things that just don't fit into the world. It's all part of the process. Today I will lay out the personal lives so-and-so monarchs of so-and-so minor nation; tomorrow I might do a little work on the linguistics of a certain language group; the next day I might figure out how the economic collapse occured in X Empire; the day after that I might dabble a bit in the prehistorical tribal society of culture Y; and so on and so on. Little things at a time. After a while, it'll build up.
Anyhow, again, my suggestion is to join some forums that deal with conworlding (or geofiction, as a few have called it, although I thikn conworlding is more common). Many of the members on these forums have considerable experience with creating these worlds and the knowledge that might be needed (though, again, you don't
need to know everything to make what you consider a believable world - you just need enough for what you want).