The series consists of seven books, published from 1994 to 1999  by Pan Macmillan and has been reprinted sixteen times. A follow up series entitled the "Ellie Chronicles" began publication in 2003  and was completed in 2006. It deals with the aftermath of the war and Ellie's attempts to regain a normal level of functioning in the face of the psychological damage sustained during the war.
The invading nation is never specified in the book; in fact, no nation in the world meets the criteria laid out in the series  most likely by explicit intent of the author. Likewise, no parts of the war outside Ellie's immediate perspective are covered; the reader is not informed exactly how much of the country is under enemy control, or how well the war is going for the Australian military. This was likely Marsden's intention, given that the series focuses on the characters more than the actual war, and is an accurate reflection of how Ellie and her friends are isolated and cut off from outside communication.