The 'Initiation Series' encompasses the first five books of the 'Terran Chronicles' saga. Book one covers our 'First Contact' with an alien race. From this spring's forth an age of 'Discovery' as we learn how to use much of the alien technology. This allows us to set up a 'Colony' or two, and then we become part of an 'Alliance' that is unprecedented in Earth's history. The last book of the first series delves into the 'Voknor Diaries', in which we follow the experiences of the Gamin leader whose fate is ever intertwined with our own.
During the 'Initiation Series', we learn how the Gamin/Atlan war came to be.
The next five books constitute the 'Survival Series'. This series begins with 'Remnants', and culminates with book ten, the 'Atlan Prophecies'. During this series we learn why the long lasting war started, and how it is that we came to be a part of it. I don't want to give away too much about the second series, other than to say that once again humanity's very future is in doubt as we struggle to cope with newer and more powerful threats.