The phrase refers to a groundbreaking work of photojournalism and social commentary published in 1890 by Jacob Riis. It meticulously documented the impoverished living conditions within the tenement districts of New York City during the late 19th century. The work visually exposed the harsh realities faced by immigrants and the working class, including overcrowding, disease, and lack of sanitation. Riis used photographs and detailed descriptions to illustrate the plight of those dwelling in these deprived environments.
Its significance lies in its powerful influence on Progressive Era reforms. By bringing the stark realities of poverty to the attention of middle and upper-class Americans, it fueled a movement for social change. The book spurred public demand for improved housing regulations, sanitation improvements, and the eradication of child labor. It served as a catalyst for legislative action and philanthropic initiatives aimed at ameliorating the conditions of the urban poor. The work challenged prevailing social attitudes and promoted a greater understanding of the systemic issues contributing to poverty.