"Blood and Iron" is the first of the author's interwar trilogy. It's set between 1918 and 1923. The series is based on the idea that the Confederacy won at Antietam, won the Civil War, won what is called the "Second Mexicn War" 20 years later, and while allied with hardly mentioned France and Britain lost to a Teddy Roosevelt-led USA allied with the German Empire ("Kaiser Bill" is still in charge Over There as the trilogy commences).
This series is pure alt-hist. No invading space aliens, no magic; and it contains all the plusses (and alas the minuses) Mr. Turtledove's readers have come to expect. We have the usual vast array of characters, most of whom are carried over from the WWI trilogy, from different social classes and different parts of the alternate world (among my favorites are Lucien Galtier, a farmer in what is now the free repubic of Quebec and the delightfully revengeful South Carolinian Anne Colleton, who's lost her plantation to an uprising by black communists in the previous trilogy and now schemes with a crackpot facist, Jake Featherston, to gain power). Most of the characters are fictional, although Upton Sinclair appears here as a Socialist candidate for president of the USA and, in the most interesting flight of his imagination, the author imagines General Custer had never met up with disaster at Little Big Horn and has survived until the 1920s, where he is engaged in fighting terrorism in USA-occupied Anglophone Canada at the age of 80.
Those are the plusses. As for the minuses, well--Mr. Turtledove just can't do sex and he really shouldn't bother (just put in three dots when the hot stuff starts and move right along please) and while he tries to be helpful to the reader, reminding who this particular character is (and some of them reappear only 80 pages apart), we do not need to be told that Custer's adjutant is overweight every time he puts in an appearance, nor that Boston factory-worker Sylvia Enos paints red rings on yellow galoshes. Then, too, while the problems the author poses are often fascinating, his solutions are sometimes too simple (a criminal case is made to disappear with amazing ease).
Fans of alt. hist. in general, and fans of Mr. Turtledove are unlikely to be deterred by these minor annoyances, however.