I've already written a stack of parallel world stories, including one where Alan Turing went to the US instead of committing suicide, one where tougher US gun laws meant that JFK, Lee Harvey Oswald and J.R. Tippitt were still alive in 1980, and one in which the Twin Towers still existed at the end of 2001. Unfortunately, that one was rejected by editors as too political...

http://stephen-dedman.livejournal.com/1674.html