If the show is true to the books, it's fiction in the sense that individual characters and minor events are made up, but the historical setting and major events

If the show is true to the books, it's fiction in the sense that individual characters and minor events are made up, but the historical setting and major events are close to accurate. After all, you can't realistically make it completely historically accurate down to the names of minor characters, simply because they weren't documented (or the documents didn't survive).