History is an integral part of worldbuilding. Now, that doesn't mean you have to hash out 10,000 years of Everything That Happened to be able to write your story... and more importantly, if you do, you certainly don't have to fold it all into your novel.* But regardless of how much detail you put into it, history comes from a specific point of view.
Of course, you can take the point of view of an omniscient, neutral narrator-- no sides are taken, telling the history as pure fact. But odds are, even if you are aiming for that, you won't quite hit it. Almost any history will take the form of one side's narrative. Point of view is everything: nobody thinks that they are the "bad guys" in a war.
So that was what I struggled with when I wrote up my histories: who's point of view is this? I decided that even though I wasn't writing just the history of Druthal, I would write from the Druth perspective. Specifically, from the point of view of a Druth scholar striving for academic neutrality, even if he would never quite hit it. But, of course, he'd have his biases. He'd have what he'd learned, written by the victors. Was Shalcer, The Idiot King really an idiot? Was King Cedidore the Mad truly isane? Or was that the narrative they'd been assigned by those who ousted them? And that goes for the victorious side as well: were the Grand Ten really ten, ambitious people with vision who strove to create a better nation? Or were they folks who were in the wrong place and did what they could to save their own skin?
This does come into play in the writing. Characters in Way of the Shield are familiar with their history-- or at least the version of history they're comfortable with-- and are doing their best to shape their actions based on how history would interpret them, with the presumption that their side is the righteous, victorious side.
Of course, there will always be other sides of history. But here's the thing: you don't have to be fair. You don't have to be balanced. You can blatantly point to one side and say, "Yeah, that's who won, so they're the good guys."**
*- As a rule of thumb, one should remember that the world is bigger than your story. That doesn't mean that you need to build everything about the world that doesn't have much to do with your story... but the idea that there is a larger world beyond the scope of your story should stay in your head. I would argue that one of the underlying problems with David Eddings's The Malloreon was that it was a sequel series set in a world built to tell a single story. Thus The Malloreon was, in many ways, a warmed-over rehash of The Belgariad, because the world was not designed to support any other story.
**- Unless you want your heroes to be scrappy rebels. In which case, "That's who won. They're the bad guys."