Watt-Evans, Lawrence. "New Worlds"
Summary: A crosstime traveler offers to sell the secret to parallel worlds, and finds one with faster-than-light travel. Both sides fear the other.
Comments: Crosstimers are from world where Hitler was killed in 1923 by a thrown beer bottle, but no further development is given.
Published: In Isaac Asimov's Science Fiction Magazine, December 1991; and Crosstime Traffic, Ballantine/Del Rey 1992 (0345373952).