What if! What a wonderful phrase, I like to read alternative history, for me it's usually Science Fiction but it has to written by someone who knows history and the events and forces that drive history. Harry Turtledove has made alternative history into an art form, he has written so many books and series of books it's difficult to keep track but my fav series by him is the WorldWar series. The split in history happens in during WW2 when aliens invade! This series eventually ends up being 9 books long ( I wish it had been 18 books! it was a great read! ) he is often considered the master of Alternate history fiction. Another very good alternative history authors is S.M. Stirling, one of his best books is "The Domination" a great alternate history that splits at the time of the US civil war.