Worldwar: In the Balance is an alternate history and science fiction novel by Harry Turtledove. It is the first novel of the Worldwar tetralogy, as well as the first installment in the extended Worldwar series that includes the Colonization trilogy and the novel Homeward Bound. The plot begins in late 1941, while the Earth is torn apart by World War II. An alien fleet arrive to conquer the planet, forcing the warring nations to make uneasy alliances against the invaders. Meanwhile, the aliens, who refer to themselves as the Race, discover that their enemy is far fiercer and more technologically advanced than expected.
After arriving in the Earth's solar system, the Conquest Fleet's essential personnel are awakened from cold sleep after a twenty-year journey originating from Tau Ceti II. Fleetlord Atvar is busy making final preparations for the invasion of Earth, expecting a rapid victory over the primitive beings that populate the planet. He is interrupted by a communications officer who reports that radio emissions are emanating from Earth. Atvar refuses to believe the report since the most recent intelligence, gathered from a probe that visited Earth in the 12th century, indicates that the inhabitants are a pre-industrial species.
The Conquest Fleet reaches Earth orbit in December 1941 and begins surveying the planet. They are shocked to find that in the course of only 800 years the inhabitants have moved from a primitive agricultural society to an industrial civilization. The Race's technology has hardly changed in more than 50,000 years and other known intelligent species are similarly slow to evolve.
After six months of reconnaissance and intelligence gathering, in May 1942 Atvar consults with the Shiplords of the Conquest Fleet. The troops have been awakened from cold sleep and are prepared to commence with military operations. However, it is within Atvar's power to cancel the invasion. Unwilling to call off the attack and face the Emperor back on Home, Atvar orders the assault to begin. Shortly thereafter the Race detonates several atom bombs above the Earth's atmosphere in an attempt to disrupt human communications. The attack begins.