Rise of the Faithful by D.S. Edwards

When America is attacked by an ancient enemy, society is left in ruins. The once great cities filled with entertainment, art, and every desire of man are turned into devastated neighborhoods ruled by the gangs that once roamed their ghetto streets. Soon, the gangs resources begin to run dry. With no knowledge of how to produce food, obtain water, or live independently, they begin raiding the countryside to take from those who do.