I’ve finished two books of this kind in the last month: The Man in the High Castle by Phillip Dick and The Years of Rice and Salt by Kim Robinson. Thoroughly enjoyed them both and want to explore this kind of theme of books more. Any recommendations?
That’s pretty much Harry Tutledove’s entire output.
Fatherland by Robert Harris and Resurrection Day by Brendan DuBois are both really good.
You might be interested in the 1632 series, by Eric Flint and assorted co-authors. The premise is that, for unexplained reasons, an entire modern West Virginia town is transported back in time into the middle of Europe in the Thirty Years War (actually, he does spend about a page on explaining it, but none of the characters knows the explanation, and it never becomes relevant). The “uptimers”, with their knowledge and technology, quickly become a major power, and start changing the course of history.
Second vote for Fatherland. If you watch the HBO adaptation of it, ignore the ending.
There actually is an award given for this particular sub-genre.
I recently finished Matt Ruff’s “The Mirage” which is an alternate take on 9/11. Thought it was pretty good.
If you’re a Star Trek fan, there have been, I think, three collections of “Myriad Universe” stories which do that same sort of thing within the confines of the Trek universe.
Oh, and Harry Harrison’s “Stars and Stripes” trilogy.
I really enjoyed Randall Garrett’s Lord Darcy stories. There are two fantastical premises: first that England won the 100 years war and England and France are a joint kingdom and second that magic is real and scientific. The actual stories take place in the 20th century, but electricity has not been discovered. There are, for example, trains, but gas lighting is used everywhere.
There is an anthology called Other Earth’s edited by Nick Gevers and Jay Lake. It has 11 short stories, of which three IMHO more than justify the cost (the other stories are of various levels of bad to ok) and are really outstanding.
Its contents are as listed below but the top three in the list are excellent reads:
• Robert Charles Wilson: This Peaceable Land, or, The Unbearable Vision of Harriet Beecher Stowe;
• Alastair Reynolds: The Receivers;
• Lucius Shepard: Dog-Eared Paperpack of My Life;
• Jeff VanderMeer: The Goat Variations;
• Stephen Baxter: The Unblinking Eye;
• Theodora Goss: Csilla’s Story;
• Liz Williams: Winterborn;
• Gene Wolfe: Donovan Sent Us;
• Greg van Eekhout: The Holy City and Em’s Reptile Farm;
• Paul Park: A Family History; and
Benjamin Rosenbaum: Nine Alternate Alternate Histories
I’d second Harry Turtledove, he has a wide variety of alternate earths in different periods to choose from, including historical, World War era, and so forth.
I’d add S.M. Stirling, both for his Island in the Sea of Time Trilogy (modern day Nantucket is send back to Bronze Age Earth, and societies interact and develop, many similarities to the 1632 series mentioned upthread), and Conquistador (a WW2 vet, freshly discharged, opens a portal to an alternate but contemporary earth where there was no industrial revolution and no contact with the Americas, and, well, the rest would be telling. 
)
The absolutely marvellous Jonathan Strange and Mr Norrell is set in a slightly askew Georgian England (and Europe) and is well worth anyone’s time, if you’re up for a very solid read (with footnotes, even!)
The Fall Of Frenchy Steiner by Hilary Bailey
The Iron Dream by Norman Spinrad
-cover similar territory to The Man In The High Castle. Read them decades ago. In truth, I don’t know what I would think of them now. I assume both are long out of print, but if you’re lurking in second hand book shops…
Incidentally, the wiki page for the latter led me to this: Hypothetical Axis victory in World War II - Wikipedia
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William Sander’s Journey to Fusang.
I think Little_Nemo and I have disagreed on these before. The first is terrific (about Nazi Germany winning WWII, and a SS investigator looking into the mysterious deaths of senior Nazis during the leadup to a 1964 Berlin summit meeting between Hitler and President Joe Kennedy Sr.); I was very unimpressed by the second (about the Cuban Missile Crisis leading to WWIII, and its aftermath).
SS-GB by Len Deighton is a chilling novel of London in late 1941 under Nazi occupation after a successful German invasion. Good stuff. The BBC did a pretty good miniseries adaptation a few year ago.
Dominion by C. J. Sansom is similar, and also very good, but it’s set in 1953 and has a significantly different plot.
Bring the Jubilee by Ward Moore is about a time-traveling historian inadvertently changing the course of the Battle of Gettysburg, and thus the Civil War. The twist is that his timeline is the original; ours is the different one.
Enthusiastically seconded. Magic inexplicably returns to England after several hundred years, and two very different men try to figure it out. A friend aptly said it was “as if Jane Austen wrote a Harry Potter book.”
Stephen Fry, the former host of QI, actor and other things, also wrote several novels. One, called Making History, is an alternate history story.
Ash: A Secret History, by Mary Gentle, is mostly set in an alternate 15th Century, following the adventures of Ash, a female mercenary captain, who fights the forces of a Muslim Visigothic Carthage that threatens Europe with invasion and eternal night. And magic and miracles work. And the Muslim Visigothic Carthaginians have golems. There is also a framing device about a contemporary archaeologist from our history who is excavating the remains of the Carthage from the alternate history. And it gets weirder from there. If you like alternate histories by way of reality quakes, it’s really good.
I cannot stand Turtledove. While his concepts are great, his writing is turgid to say the least. It is unreadable to say the most.
I like him more than that, but yeah, he’s better with big ideas than with dialogue or characterization. How Few Remain is his best Civil War alt-hist novel, I’d say. As with the best such books he takes, as his departure point from our timeline, an actual incident that could easily and plausibly have turned out differently: Special Order 191 - Wikipedia
Perhaps not exactly alt-history in the sense that there’s no specific event which precipitates the divergence, but Poul Anderson’s Operation Chaos and Operation Luna are set in a world in which people discovered how to “degauss” the ruinous effects of cold iron on goetic forces around the beginning of the 20th century. As a result, much of what we use machinery and/or technology to achieve is done with magic: for example, broomsticks and flying carpets are used instead of cars and airplanes. Also, the hero is a werewolf and his wife — the more dominant of the pair — is a witch.
(An implied side effect is that all the ghoulies and ghosties and long-leggity beasties that had been sleeping since the end of the Bronze Age woke up along with more benign spirits, and it took a great deal of effort to get them under some form of control.)
The first book is a quicker read since it’s an anthology of short stories. The latter is longer and much more dense, partly because it’s a more intricate story and partly because it delves into a fair amount of backstory. It also displays much more of Anderson’s libertarian outlook, which gets in the way of the plot at times; still, I found it a very satisfying read.
The Gate of the Worlds by Robert Silverberg.