The Collapsing Empire by John Scalzi
The Collapsing Empire (The Interdependency)
Our universe is ruled by physics. Faster than light travel is impossible―until the discovery of The Flow, an extradimensional field available at certain points in space-time, which can take us to other planets around other stars.
Riding The Flow, humanity spreads to innumerable other worlds. Earth is forgotten. A new empire arises, the Interdependency, based on the doctrine that no one human outpost can survive without the others. It’s a hedge against interstellar war―and, for the empire’s rulers, a system of control.