Now I'm older, and amazingly I'm starting to go in the opposite direction. I'm currently reading Horror on the Orient Express, a massive campaign for Call of Cthulhu. It takes place in 1923, and has the players solving a mystery throughout Europe, starting in London and ending in Constantinople. Young Ed would have immediately written this whole adventure off as a snooze fest. But present-day Ed is enjoying the hell out of it. There is so much flavor, so much history, so much setting in this campaign!
And then I think about the rest of the world. I think about the Revolutionary War, the Civil War, the World Wars, and the Wild West. I think of the Great Depression and feudal Japan. The history of the world is ripe for adventure. Now, I wonder why so much time and energy is spent on fantasy when real history has so much to offer!
When I think of resistance to playing a game set in history, my first thought is about historical accuracy. It's easy to make up a fancy little history for a bunch of pointy-eared elves that never actually existed, but it's harder to, say, get the details right on 1920's era French socialists. My plan for this whenever I get a historical game to the table is the same as for any fantasy setting; I'll do some research, give it my best shot, and bullshit my way through the stuff I don't know. When it comes to RPGs, it's the adventure that's the thing, not historical accuracy. As long as I keep the story moving and the dice rolling, I doubt anyone's going to care much if I properly pronounced some French landmark (and if they do, I probably don't want them at my table, anyway).
Branching off that point about historical accuracy, I think a lot of GMs may have this perception of a lack of freedom in designing an adventure in a historical time period. But to that I say the same thing I said at the end of the last paragraph: keep the story moving, keep the game flowing, and no one should care all that much. It's the same with movies, right?
Another apprehension some may have is not knowing what a certain historical period looked or felt like. It's easy to look at some pictures of dwarves and castles and just have an idea of what life must be like in that particular fantasy world, but what was London in 1923 like? What does a street corner look like in Constantinople? To that, I offer the pragmatic answer: it looks just like it looks now. That's all. Unless you have evidence to support otherwise, just visualize the world you know, or at the very least, the world you conceive of. If I say your party is in a market in downtown Constantinople, just picture a market. It doesn't have to look or feel any different than any other place. It probably does, of course, but if you don't know and I don't know, then who cares? The point is, I don't think we should let our ignorance of a sense of place prevent us from exploring that place in our minds.
And, in the rare instance when you have someone at the table who's been to Constantinople (now known as Istanbul)? Use that person's knowledge! Put them on the spot, tell them to describe to the table what a market looks like. If they don't know, then you're no worse off.
Using history in today's games is especially fun now thanks to the Internet. As I read Horror on the Orient Express, I'm constantly Googling references made to all kinds of historical stuff. In game, if the players end up jumping off the page and exploring some part of Europe or Asia or whatever that you're not prepared for, call a quick ten minute break and whip out your smartphone. Jot down some notes, and keep going!
The last point I'll bring up is, to me, the hardest: cultural sensitivity. World history has not been kind to many an ethnicity. There are several options for dealing with this, but I think the important thing is to communicate very clearly with any players who may be affected by this and work together on what you're going to do. In my Cthulhu games, I've been lucky enough to have several female gamers. Rather than deal with the sexism that was inherent to the 20's, I tend to conveniently just ignore it. This doesn't really seem to affect anything, in game. In fact, the only time I've ever brought race into a game is when a player was being coerced by a cultist to kidnap people for a human sacrifice: the cultist suggested gathering black people, since they wouldn't be noticed as much if they went missing. I did this on purpose to tip the player off that who he was dealing with was a bad person, since he didn't seem to be getting it from some of the other clues I dropped earlier in the adventure. Nothing says "clearly evil" like a racist NPC!
Anyways, I'm not saying I've become a history buff now or anything. I'm just saying that I'm giving world history a chance, and I'm finding it rather interesting.