This is a question that I just had tonight before I went to bed. Later this week, I intend to answer it more fully than I will here. But, here is the thrust of my question: "How much history does my fictional world need to maintain realism, allow the audience to suspend disbelief and give me enough material to write fluidly?"
In my longer post, I plan to take a look at different kinds of fiction, different audiences and different purposes for writing. Right now, I want to outline a few general rules.
Small Scale, Recent History
Your characters (or NPCs) need enough history to be doing reasonable things when not on stage and before they came on stage. What did Macbeth do while his thugs were killing Macduff's family? What was he doing before he met the witches? If I ask you what a character did between chapter two and four, you need to have an answer.
Major recent political events do not need to be referenced, but they should inform your writing. Was there a coronation? Did we discover FTL transit? Were certain kinds of robots recognized as sentient creatures? How does this impact your characters?
Long Term, Political History
Do your characters live in a republic? Under a tyrant? A generational lord? Does magic exist (this will greatly impact politics)? Is there interstellar travel? How are aliens treated? What major laws, wars, events or movements should people be passingly familiar with? For example, most people are aware of the signing of the Magna Carta, even more of the Declaration of Independence. Are there similar cultural touchstones that your fantasy world can have?
Here is where in our high fantasy that prophecies and religious and arcane mysteries fall. Is there an arc of history? In Arcanum, for example, you are during a technological revolution bringing an end to the age of magic. The whole design and feel of the world is informed by this long term historical choice.
So, how can you use history to actual inform your writing? We'll come back to that later this week.
I have one story that I'll use to examine it, which is the one that I've just finished an early draft of. If you want to read that story to be able to understand what I'm talking about, look me up on Google+, Twitter or somehow let me know, and I'll send you the current draft version.