Part six of my fantasy overview.
Some authors write works set in our world's past, with varying levels of fantasy elements. For the authors I've listed, these are enjoyable on a direct level but even more so if you're interested in the history involved. Steampunk is included in the same category because it is based on a Victorian sensibility, making it at times difficult to separate from alternate history titles.
Phil and Kaja Foglio
Best known for their Girl Genius series of graphic novels, they're a good example of why steampunk often falls into the fantasy genre. They actually call their work (a pseudo-Europe ruled by mad geniuses capable of turning a toaster into a ray gun and also a better toaster) "gaslamp fantasy" because it uses the Victorian aesthetic with relatively little connection to actual science.
Arguably steampunk, in The Half-Made World Gilman presents a world with a broad and unformed frontier. Civilization presses into wild territory as a war continues between sentient engines and agents of ancient spirits. This book is refreshingly different and the series promises to go interesting places.
Guy Gavriel Kay
He generally takes historical events and reshapes them into a fantasy story. Things do not progress according to history, but they do shed new light on the actual events. His books also tend to stand alone, and there is significant focus on craft at a prose level.
Direct historical fantasy: her major series is an alternate history of the Napoleonic wars, shaped by the inclusion of dragons as air support. There is no other magic and as you'd expect the series has a military tone and focuses on human/dragon interactions.
Though his work isn't always shelved as fantasy, it has appeal for any speculative genre reader. His books are alternate histories, weaving magic and invented characters around established facts. Even if you don't want to read about a brainwashed clone of Lord Byron (why not?), there are insane clowns and magic pirates and elementals.
Imagine WWII, dragons replacing aircraft, leviathans replacing submarines, and magic replacing bombs. Turtledove has written broadly, including straight alternate history, but his "Darkness" series of fantasy WWII books is a good example of fantasy with heavy historical elements. It draws strength and interests from historical analogues while presenting a fresh take on the events.
Another author sold as YA but enjoyed by many. His Leviathan series is an alternate World War I, Darwinist countries using genetic manipulation to create animals for war and Clanker countries creating mechs and other steampunk technology. Sharp and fun, and involved in many interesting historical details.