I’ll come right out and say that when I’m reading a fantasy book set in a time and place analogous to real human history (and aren’t they all?) I expect some level of ‘historical accuracy’. 

The right amount of historically accurate details judiciously applied is the sprinkling of salt that makes the butter of a story taste like heaven. It helps to create reader immersion. In the same way I wouldn’t step into a lift made of papier mache, nor would I want to spend time in a world that doesn’t feel solid beneath my feet. There might be roads in this land but if they’re made of asphalt by a society that hasn’t discovered petrochemicals, you’re going to sink right through a surface that has no basis to exist. 

Same goes for anything else. How are these characters wearing cotton in a land that doesn’t support the cotton plants’ ideal growing conditions? How can we be eating a fluffy sponge cake in a world with inconsistent oven temperatures and no sugar? I always want to ask the question: where did it come from? Who sewed these clothes? Who grew that food? Who prepared it? In what? With what utensils? Is there enough to go round? Even if these details never come up, I want the book to give me all the right clues to say the writer knows the answers and I can continue reading, secure in the knowledge that the food on the plate before me is not merely for show but made with real ingredients. 

Those clues might come in the form of fields of crops or livestock lining the roads, of markets and ports and all the people needed to make those places work. I want scenes filled with ordinary people going about all the mundane everyday jobs necessary for the main characters to pursue their grand adventures without starving to death with no clothes on. 

Another key element of reading fantasy books to me is the opportunity to learn something. I love learning about historical details even in fantasy books. Even though the ships in Robin Hobb’s Liveship Traders series were magical and ‘alive’ I could tell through reading that the author had actually researched the design and operation of real sailing ships to use in the story and that made the experience of reading all the richer. In this way I also like the author to credit me with enough intelligence to discern what’s historical fact and what is unique to their world. I might even be prompted to go do a bit of research of my own. But even unique details must have causality, must have a reason to exist in the world of the story. A city’s strange architecture might be the product of an ancient technology that no-one living understands but the author does -or should. An author’s understanding of their own world is the iceberg hidden below the surface that the reader never sees but must believe is there so as not to scupper their ship then flounder in a sea of implausibility. 

 But then we come to the poisoned chalice of ‘historical accuracy’ in fictional societies. If I read a book that contains classism or racism or sexism ‘just because’ and doesn’t address why the characters accept (or rail against) this way of living, I don’t feel like I’m in a real place and I will put down the book and walk away. People have always been aware of injustice, they just didn’t have the same words that we do nowadays to talk about it. It’s not that they didn’t notice they were at the bottom of the heap; they knew but believed it was what ‘god chose for them’ or ‘just the way things were’. If there is inequality in a fictional world I want to see how it’s reinforced, either by laws or religious teachings or even by deliberate lies told to turn one community of people against another. Oppressive social structures often come about because they provide some sort of benefit as well, like providing free labour to create wealth for those in power.
 
Just as in the real world, oppression in a fictional world should not go unnoticed by the characters. Whether it’s classism, racism or sexism everyone has to pick a side. Some characters will just go along to get along, some will be active participants and others will rebel. A peasant lamenting their lowly lot in life and plotting the murder of his lord and one happily tugging his forelock and feeling lucky to be able to clean his master’s boots are both a product of the same society, brought to their individual beliefs by their own unique life experiences. Incorporating these different attitudes adds rich layers to characterisation, world building and story telling. 

It doesn’t have to be heavy-handed, it doesn’t have to be what the story is all about, but I think a full-bodied story taking place in a well-built world will come with these things as standard. Nobody wants to be beaten around the head with an author’s great compendium of research into 14th Century east-anglian farming practices. Just little hints and nudges that show that this is world made up of believably real people, flaws and all.