The Necessary War

On the first day of an alien invasion, Greg Sims is taken prisoner. Dumped in a holding cell, he decides to fight the war using any weapon he might find.  Soon Greg learns that his best weapon is the ideals and concepts that are foreign to his captors.  As a result of his efforts, an insurrection begins among the species that have captured him. As Greg fights his war, humans find ways to set aside their differences and fight a common enemy.
In the end, Sims discovers a surprise reason why the war started at all.