The king of Darwin in the most recent SM Stirling books is referred to as “JB” and is, in fact, John Birmingham.
I liked Peter Tsouras’s Civil War trilogy “Brittania’s Fist”.
From Civil War to World War
A Rainbow of Blood: the Union in Peril
Bayonets, Balloons & Ironclads: Britain and France take sides with the South
The point of divergence from real history is shortly before the escape (and transfer to the CSA) of one of the Laird Rams.
I’m assuming you figured out that Ian Arnstein is also a homage to Harry Turtledove.
Another not-a-series, but I enjoyed Philip Roth’s The Plot Against America, where Charles Lindbergh is elected President in 1940 and forms a non-aggression pact with Hitler. This is straight alternate history with no sci-fi or fantasy elements.
I keep wanting to read Ian Tregillis’s “Milkweed Triptych,” which starts with Bitter Seeds, which sounds like an interesting premise, where the Allies and Axis Powers are both working on superpowers or something, but I haven’t gotten around to it.
Are there more books beyond Guns of The South with the premise that slavery in the US didn’t end in 1865?
How about alt history books set now-ish after a fairly recent divergence in time, like say after 1970?
wiki:
*The Confederacy wins the American Civil War in 1862 with the help of the United Kingdom and France. It still operates as an independent nation in the 20th century. Another popular moniker for this series is Timeline-191.
How Few Remain (1997)
The Great War trilogy
American Front (1998)
Walk in Hell (1999)
Breakthroughs (2000)
The American Empire trilogy
Blood and Iron (2001)
The Center Cannot Hold (2002)
The Victorious Opposition (2003)
The Settling Accounts tetralogy
Return Engagement (2004)
Drive to the East (2005)
The Grapple (2006)
In at the Death (2007)
All by Harry Turtledove of course. The best being the first one, How Few Remain.
I’ve got one that sort of fits, since you liked the fantasy turn that the Emberverse series by Stirling took.
Jim Butcher wrote a series of books based on the premise that a Roman legion somehow ended up on another planet. The series is about their society approximately 1000 years later. The series is called Codex Alera. There are 6 in all. I personally like books 3-6 best, but they are all good.
Fatherland by Robert Harris - Chilling alternative history about a murder investigation in 1964 Nazi Germany.
If the South Had Won the Civil War by MacKinlay Kantor - An interesting and largely plausible examination of how the Confederacy might have triumphed.
Bring the Jubilee by Ward Moore - A bit dated now, and not as plausible as Kantor’s book, but worth a look. Best idea: Our world’s timeline, with a U.S. victory in the Civil War, is the alternative history.
Elleander Morning by Jerry Yulsman - Clever, engaging sf novel about a woman who goes back to kill Hitler while he was still a starving artist in Vienna.
The Court-Martial of George Armstrong Custer by Douglas C. Jones - What if Custer survived the debacle at the Little Big Horn? Great courtroom drama.
SS-GB by Len Deighton - Gritty tale of the UK under German rule after a successful invasion, with Churchill executed and King George VI under guard in the Tower of London.
I should add:
Jonathan Strange & Mr. Norrell by Susanna Clarke. Magic returns to Regency England after centuries. Great book, with incredible world-building - almost as if Jane Austen wrote a Harry Potter book.
Watchmen by Alan Moore and Dave Gibbons - Classic graphic novel. What if superheroes were real? The U.S. wins in Vietnam, Woodward and Bernstein are murdered, and Nixon gets reelected again and again and…