I agree with you on the excellence of Newt Gingrich and William Forstchen’s 3 volume alternate history of the Battle of Gettysburg.
As for straight alternate or counter-factual military histories without the ‘political bent’ of most science fiction “alternate history” writers I highly recommend the books written by Peter G. Tsouras. He is a retired Army lieutenant colonel and military intelligence analyst (Soviet & Warsaw Pact). His focus is on “what if another decision had been made” by commanders. He has also written several non-fiction books on military history.
I also enjoyed retired British general Sir John Hackett’s two volumes on “The Third World War.” Although I’m a bit bias because I was a captain with the 3d Armored Division sitting 60 miles west of the Fulda Gap when it was published in 1985.
Just looking at a map of Germany/France from the 1840’s (all of the hundreds of principalities, duchies, and communes which all disappeared as a result of WWI). And the Fulda Gap— which was a major route to be defended against a potential Soviet wave (tanks, infantry) major Cold War attack, coming from East Germany, in the 1800’s was internal to the German Confederation.
Interestingly the Fulda Gap never featured as a defense position in that Confederation, because any Russian or whatever attack had it reached that far in to Germany would mean the defeat of Germany. The presence of two routes through Fulda and Alsfeld, both cities in Hesse-— is the reason for the power that Hesse retained all through those years and into WWI and II.
Frederick the II, Landgrave of Hesse rented out thousands of the professional soldiers he maintained for just that purpose the mercenary (King owned- important point) Hessians who the British brought to America and whom Gen. Washington defeated completely at the Battle of Trenton on Christmas day. Also- many of the Hessians faded away during the end of the Revolutionary War to remain in the new frontierland (like in North Carolina) who were miners (gold), and there is Mecklenburg (like the German state) county/Charlotte of today. Lot’s of those Hessians stayed around, and joined the many German protestants who had escaped Euro-Monarchists and zero future.