The book "The Dangerous Classes of New York, and Twenty Years of Work Among Them" by Charles Loring Brace is an important document about the social problems of the 19th century in the United States. The author examines the lives of the poorest strata of New York's population, their problems, living conditions and social conditions. Brace talks about his twenty years of work among these classes, trying to find out the roots of the problems and suggest ways to overcome them. This book helps to better understand the social aspects of the life of the inhabitants of big cities and the challenges that the urban population has to face.