Worldwar

Worldwar is a series of novels by Harry Turtledove whose premise is an alien invasion of Earth in the middle of World War II. The military invasion begins on or around May 30, 1942, but the aliens, who call themselves the Race, reached Earth orbit in December 1941.

Although the Race, a reptilian species, has the advantage of superior technology, their information on humans was collected by a robotic probe during the 12th century. The invaders are surprised to find that humanity has progressed far more rapidly any other species they had previously studied. Contrary to their expectations, at the time of invasion the Race's technology is only marginally more advanced than current 20th century Earth technology.

The narrative follows the intersecting fortunes of a large number of human and alien characters. Notably, the series depicts how the Axis and Allied powers must cooperate to fight the alien menace.