The Final Day by William Forstchen.
This was the A John Matherson Novel. The Third in the series.
Here is the description from Amazon:
Since the detonation of nuclear weapons above the United States more than two years ago, the small town of Black Mountain, North Carolina has suffered famine, civil war, and countless deaths. Now, after defeating a new, tyrannical federal government, John Matherson and his community intend to restore their world to what it was before the EMP apocalypse. For the most part, they are succeeding.
This period of relative stability doesn’t last long. A new, aggressive government announces that it’s taking over and ceding large portions of the country to China and Mexico. The Constitution is no longer in effect, and what’s left of the U.S. Army has been deployed to suppress rebellion in the remaining states. John fears he and his town will be targets.
General Bob Scales, John’s old commanding officer and closest friend from prewar days, is sent to bring John into line. Will John and his people accept the new, autocratic regime? Or will revolution rip the fledgling nation apart at the seams?
Months before publication, William R. Forstchen’s novel One Second After was cited on the floor of Congress as a book all Americans should read. This third book in the series immerses readers once more in the story of our nation’s struggle to rebuild itself after an electromagnetic pulse wipes out all electricity and plunges the country into darkness, starvation, and death.
--If you have not already, read One Second After.