Daybreak Zero by John Barnes

A year has passed since "Daybreak" when techno viruses were unleashed into the atmosphere, destroying everything electronic and mechanical they contacted. The chaos and panic that followed split the United States government in two. And new societies, populated by "tribes," recognize no authority within their boundaries. If either government is going to retake the country, the United Tribes will have to be recognized. And the "Daybreakers" who caused the technological catastrophe are preparing to strike again.