Colonization: Down to Earth is an alternate history and science fiction novel by Harry Turtledove. It is the second novel of the Colonization series, as well as the sixth installment in the extended Worldwar series. British editions are entitled Colonisation: Down to Earth and are the second of the Colonisation series.
Following the nuclear attack on the colonist ships in Second Contact, the Race continues to try to find the responsible nation, along with the purpose of the Lewis and Clark, a large space station launched by the United States. At the same time, the range animals brought by the Race's colonists begin to spread into the human nations, causing ecological trouble and causing conflicts between them.