This book aims to outline the detailed process of integrating nature and cities in a historical context through the lens of urban environmental history, capturing how the most ordinary yet enduring natural forces have shaped the form of cities and the thoughts of individuals. It provides a detailed examination of the development trends, achievements, and existing issues in this field, and a profound understanding of the urgency and necessity of nurturing new ideas to guide cities out of their "ecological paradox". It also summarizes the formation and development, challenges, and missions of American cities centered around the core image of the "City Without Walls".