I'm a history person (I believe I've said that before) but I am also a fantasy/science fiction reader. Actually, given my druthers, that is about all I read. Usually, I have to pick make up my mind, but every once in a while a book or series comes along that gives me a good bit of both. I really, really, like that. So, if you are a history person who likes a little sci-fi or a Sci-fi reader who doesn't mind a little history... give these a try.
This one gives you a lot of science fiction and a lot of history... readers beware Ben Jeapes's imagination is dizzying so pay attention. In The New World Order Oliver Cromwell's Roundheads are busily fighting Charles I and his royalists when they are attacked in force by the Holekhors who are intent on colonizing Great Britain. In case you missed that, the Holekhors are a race of Alien Invaders. Yep, full scale alien invasion in the middle of the English Civil War. Strangely enough, the alien invasion doesn't detract from the historical elements and the history doesn't distract from the cool complexities and imaginative elements you want in good sci-fi. On top of that he gives you likable and relateable characters in the form of Holekhor Dhon Do, who is masquerading as the soldier John Donder in England, having been there long enough to grow English sympathies and father a half-English son. This was a really neat book that history and sci-fi readers alike ought to enjoy. Have fun trying to keep the facts separated from the fiction.
If you think putting aliens in the British Civil War was fun try putting Giant Mechanized Weapons and Bio engineered Air Ships into World War I. Leviathan and it's sequel Behemoth are really something else. In Leviathan Prince Alek is on the run after his father Arch Duke Ferdinand is assassinated. He ends up falling in with a young member of the British Air Service on board a giant living air ship or "Leviathan". Deryn, the young midshipman happens to be a teenage girl. Both teens have secrets to protect and wars to fight. In Behemoth Alek and Deryn travel in the Leviathan to Constantinople and get entwined in the political intrigue of the Ottoman Turks. Both of these books take place in 1914 right at the dawn of World War I, and a lot of the events depicted were real. Scott Westerfeld just put a cool steam punk sci-fi twist on them. The characters read a little young, the science isn't overpowering, and there are enough plot twists to maintain the reader's interest. These would be great for readers who are just getting into the sci-fi genre. You don't have to know your history to enjoy these books, but those who do will find Westerfeld's manipulation of World War I events interesting.
Last but not least, I thought I would mention The Missing Series by Margaret Peterson Haddix. While the first novel in this series does not have much by way of history, the two subsequent works incorporate quite a bit. Haddix even includes historical notes at the end of them. In this series a futuristic technologically advanced society has travelled back into time to "rescue" famous children from famous fates. These historical kidnapping destabilized the time continuum and another group from the future has come to send the kids (accidentally dumped in the present as infants due to a hiccup in time) back to their fates. Time travel is a sort of obvious means of connecting Science Fiction with history, and it has been done many times. But I've always been a Haddix fan, and I think she has done a pretty great job with this series. There are some neat sci-fi capabilities in this book, in addition to time travel, the main characters can pause time... rewind, make themselves invisible, and talk to the powers that be in the future through a remote. If you are not a historical fiction fan, you might want to skip these, because both Sent (book 2) and Sabotaged (book 3) are very history heavy. If you are a history person, don't let the sci-fi elements scare you, Haddix did her research and it is easy to separate the fictional elements from the history.
No matter what I am in the mood to read, books like those above will usually work for me. If there are any other sci-fi/history enthusiasts out there, give them a try.