Both world wars, the American Civil War, the Revolutionary War, the Cold War and in one baffling instance, the French-Indian War. Basically any war Americans had been involved in, or could potentially have been involved in that weren't currently ongoing.

He snorted softly, "You're presuming anyone can parse him at any time." He nodded at the explanation, because chances were good even if that exact title didn't exist, something like it would, and it would give him something to go on no matter what library he wandered himself into. He didn't generally mind straight up historical fiction, either, as long as the author wasn't trying for a 'new' historical viewpoint that had already been done to death, "I even resorted to romance novels for a while, because at least if they're being historical, it's usually because the author actually likes the time period they're writing about." He shook his head, "But they all end up being too much like getting a lecture from Robin, and I'd rather not."