[1] Its premise is an alien invasion of Earth during World War II, and includes Turtledove's Worldwar tetralogy, as well as the Colonization trilogy, and the novel Homeward Bound.
The commander hesitates, and considers turning back without revealing The Race's presence to the humans but finally decides to avoid the disgrace of that course of action.
As is gradually revealed, the Race unified its home planet into a single state with a military technology at a level similar to our history's late 20th century.
The invasion ultimately ends with all of the major Allied and Axis powers managing to develop their own nuclear weapons, which results in a stalemate.
The Race is left in control of roughly half the planet, primarily colonial possessions in the Southern Hemisphere: Africa, South and Central America, Australia, and most of Asia aside from the Soviet Union and a few Japanese coastal holdings.
Opening with the arrival of the colonization fleet, the series ends with the defeat of Nazi Germany and the establishment of a permanently-occupied US space station in the asteroid belt.
The Race is also faced with ongoing guerilla wars in much of the territory that they conquered, especially by insurgents, both Kuomintang and Communist in China and by militants in the Middle East influenced by Khomeini.
The Race, confirmed conservative monarchists and chauvinists who take the superiority of the Empire as axiomatic, find it difficult to understand why the Big Uglies continually and constantly attempt to rebel against them, and why some of their policies (like introducing a tax on religious worship) do not work.
Another major issue turns out to be ginger, an innocent flavoring in human cuisine but a powerful narcotic for the Race's metabolism.