Saunders, Jake. "Back to the Stone Age"
Divergence: 1945 CE
What if: Disaster at Oak Ridge scrapped the Manhattan Project, and the US decided not to invade Japan.
Summary: In 1954, random bombers fly over the bombed-out Japanese islands, eliminating any signs of human activity they happen to find.
Published: In Lone Star Universe: The First Anthology of Texas Science Fiction Authors (eds. George W. Proctor and Steven Utley), Heidelberg 1976 (0913206083) and Best Science Fiction Stories of the Year, Sixth Annual Collection (ed. Gardner Dozois), Dutton 1977 (0525064958), Ace 1978 (044105482X).