Worldwar: Tilting the Balance is an alternate history novel by the American writer Harry Turtledove. It is the second book in the Worldwar tetralogy and in the extended Worldwar series, which includes the Colonization trilogy and the novel Homeward Bound. In the novel, the major world powers struggle to develop the first human atomic bombs with material taken from the invading aliens, known as The Race. Source: Wikipedia (en)