Final answer:
The challenges facing the revitalization of American cities are economic and social in nature, hindering progress through barriers to shared resources and environmental strain.
Step-by-step explanation:
The challenges facing the revitalization of American cities are economic and social in nature. Economic challenges include issues such as traffic congestion, overcrowded schools, and a widening economic gap between the rich and the poor. Social challenges arise from tensions between demographic groups and environmental strain. These challenges hinder revitalization by creating barriers to shared resources and contributing to pollution and energy use.