What was the primary subject of Jacob Riis's book "How the Other Half Lives"?

Jacob Riis's book "How the Other Half Lives" primarily addresses the living conditions of the impoverished populations living in urban slums during the late 19th century in America. Through a combination of photography and detailed descriptions, Riis exposes the harsh realities faced by these individuals, including overcrowding, unsanitary environments, and the lack of basic necessities. His work aimed to raise public awareness and promote social reform, emphasizing the stark contrast between the lives of the wealthy and those struggling in poverty. This focus on slum living conditions was crucial in inspiring later reforms aimed at improving housing and sanitation for the urban poor.

The other options do not represent the central theme of Riis's work—while factory conditions and corruption in politics were indeed pressing issues of the time, they were not the main focus of this particular book. Additionally, women's suffrage, which addressed women's rights to vote, is a separate topic and not the subject of Riis's powerful exploration of urban impoverishment.