What is the theme in The Power Broker: Robert Moses and the Fall of New York by Robert Caro?

One of the themes of the book is the value of dreams. Moses has a dream throughout his career in public service. His dream begins when he is a young man fresh out of school when he used to gaze out over the East River and dream of a great expressway. The book, and Moses' story, is the story of how he fulfills his dream. His dream involves developing a system of parks and highways for New York. Parks and highways cannot be built without money and power.