Fehrenbach, T.R. "Remember the Alamo!"
Divergence: 1813 CE
What if: Napoleon conquered Britain.
Summary: A Britisher from our (?) timeline goes back in time to the Alamo, but its defenders don't behave like history has led him to believe. Eventually, he realizes that it's not his history.
Published: In Analog, December 1961; Analog 1 (ed. John W. Campbell), Doubleday 1963 and Paperback Library 1964; Political Science Fiction: An Introductory Reader (eds. Martin H. Greenberg and Patricia Warrick), Prentice-Hall 1974 (0136554044, 013685396X); Transformation II (ed. unknown), Fawcett 1974; Robert Adams' Book of Alternate Worlds (eds. Robert Adams, Martin H. Greenberg, and Pamela Crippen Adams), q.v.; and Isaac Asimov Presents the Great SF Stories: 23 (1961) (eds. Isaac Asimov and Martin H. Greenberg), DAW 1991 (0886774780).
Original in: English.
Translation: Italian by Elisabetta Moreolo Svaluto as "Ricordati di Alamo!", in Le grandi storie della fantascienza: 1961 (eds. Isaac Asimov and Martin H. Greenberg), Mondadori 1993, 1994 (8804376740).