I would say the first three books form a series. An underlying story of a great interstellar war and how that war was first lost than won. Of course you won't

I would say the first three books form a series. An underlying story of a great interstellar war and how that war was first lost than won. Of course you won't be able to put all of this together until the last book in the trilogy, the last chapter. The other books can be read out of order, but the first three are a trilogy.