Harry Turtledove's latest book, Homeward Bound, is the conclusion to his "Worldwar" and "Colonization" series. As we join the tale already in progress, an ancient, highly sophisticated alien species sought to colonize and transform a world to its own use. Unexpectedly, however, the planet's present inhabitants weren't willing to cede their world quite as willingly as the aliens expected (nor were the inhabitants quite the pushovers the aliens anticipated). The world, of course, is Earth, albeit an alternate Earth in which aliens appeared in "War of the Worlds" fashion at the height of World War II, forcing the combatants to turn their attention from one another and battle the aliens interested in subjecting all of humanity.

Turtledove is undoubtedly the best-known author of so-called "alternate history" around today, including his Civil War tale The Guns of the South and the alternate World War I series, The Great War. In the Worldwar series, Earth's defenders find themselves faced with the challenge of fending off the lizard-like aliens called "the Race." The Race has already conquered two other planets which now reflect the staid glory of an galactic empire that has existed for hundreds of thousands of years. When they discover Earth, its population seems primitive and barbaric (little more than armored men on horses). The Race prepares a colonization force; however, in their typical deliberate manner, doing so takes several centuries. By the time they finalize their preparations and actually launch their invasion force toward Earth (at speeds of about 1/3 that of the speed of light), several centuries have passed. And during the years it takes the invaders to cross the eleven or so light years from the Race's home planet to Earth, even more changes take place on the targeted planet - changes which will have a dramatic impact upon the outcome of the invasion.

Homeward Bound opens as the aliens and humans have settled into an uneasy stalemate. It's been some thirty or so years since the invasion force arrived. The pace of humanity's development of technology meant that several nations (or, in the language of the Race, several "not-empires") were able to hold the invaders off. Among these nations was the United States. The "world war" between the aliens and humans (whom members of the Race alternately call Tosevites or "Big Uglies") ended, if you will, in a draw. The uneasy compromise has members of both species in control of portions of the planet.

The conflict, however, has an unintended consequence: humanity's native inquisitiveness now has a more immediate spur, and the Race is amazed at their ability to adapt to change. Within a few short years, Americans manage to develop their own form of cold sleep and build a spaceship, which they launch toward Home. The aliens have plenty of time to prepare for their visitors; radio signals travel faster than a space ship, after all, and as the Americans' ship travels at a slower rate than the Race's ships so it takes nearly forty years for it to arrive in the skies above Home - beaten by nearly a decade by the Race's own messengers.