Birmingham and TurtledoveEdit
Birmingham's alternate history novels resemble those of Harry Turtledove, with whom he shares much of his fan base. The Axis of Time trilogy in particular is reminiscent of Turtledove's Worldwar series. Both involve World War II abruptly being interrupted by the unexpected arrival of a large force of military personnel whose equipment derives from technology two or three generations beyond that of the 1940s, but familiar to the reader at time of publication. Both have subplots centering around social changes driven by social pressures stemming from the arrival of the science fiction contingent. Also, both are told by a large, diverse, and fairly loosely related cast of characters who tell the many contingent stories of a whole narrative. This style is also employed by Birmingham in Without Warning.
Birmingham has shown his awareness of his similarities with Turtledove through a number of fan services. In the Axis of Time books, a number of characters reacted to the incredible news of the arrival of time travellers by scoffing "Next you'll tell me space lizards will show up!" One character who says this is Franklin D. Roosevelt, who is first informed of this new development by an aide named Turtletaub, which was the name Turtledove's family used at the time.