I didn't even know alternate history existed when I made my first attemt back in 6th grade, before kids even had acccess to typewriters, a d computers were something seen on Star Trek reruns. In 6th or 7th grade English (I was born in the mid 60's, so long long ago) , we were told to write a science fiction story, and I wrote what must have been an awful alternate Battle Of Jutland. A German genius had developed a primitive radar set--just good enough to tell that there was something out there--so the High Seas Fleet was in line of battle and caught the Grand Fleet in cruising formation. The results were obvious, at least to a junior high kid that knew the cost of war--had an uncle that didn't come back froom Vietnam. War over, no USA in the war, no Hitler, and a century of peace. Obviously simplistic, but the teacher pointed me at a SC Foreser collection that had an alternate history story--the inevitable Sealion. IIRC, it failed badly. That got me interested in the genre, when I could find anything of it--small town library...
So alternate history has been around for a long time
So alternate history has been around for a long time