Sunday, April 14, brings the long-awaited premiere of the eighth and final season of “Game of Thrones,” HBO’s megahit adaptation of A Song of Ice and Fire, the best-selling fantasy series by George R.R. Martin. For those unfamiliar with the show, it’s probably best described as Machiavellian realpolitik meets the Wars of the Roses but with dragons. Since premiering in 2011, it has become one of the most popular shows of the past 20 years, with roughly 31 million average viewers per episode last season, according to Vulture. But it’s also something more than that. For the better part of a decade, “Game of Thrones” has been the most vividly engaging history course millions of Americans have likely ever received, whether they realize it or not. For instance, if I asked you to describe the Second Arab Siege of Constantinople in 717, could you? Probably not, even if you’d learned it in school. But if you’re a fan of “Game of Thrones,” or, better yet, had read the books, and I told you it was the basis for the second season’s Battle of Blackwater Bay, you’d know, more or less, what took place between the Umayyad Muslims and Byzantine Christians at Constantinople: Forces defending a fortified capital city were able to repel an invading army on both land and sea, thanks in large part to the use of a massive chain boom that blocked naval...