Starr and Addams developed three "ethical principles" for social settlements: "to teach by example, to practice cooperation, and to practice social democracy, that is, egalitarian, or democratic, social relations across class lines." Thus Hull House offered a comprehensive program of civic, cultural, recreational, and educational activities and attracted admiring visitors from all over the world, including William Lyon Mackenzie King, a graduate student from Harvard University who later became prime minister of Canada. In the 1890s Julia Lathrop, Florence Kelley, and other residents of the house made it a world center of social reform activity. Hull House used the latest methodology (pioneering in statistical mapping) to study overcrowding, truancy, typhoid fever, cocaine, children's reading, newsboys, infant mortality, and midwifery. Starting with efforts to improve the immediate neighborhood, the Hull House group became involved in city- and statewide campaigns for better housing, improvements in public welfare, stricter child-labor laws, and protection of working women. Addams brought in prominent visitors from around the world, and had close links with leading Chicago intellectuals and philanthropists. In 1912, she helped start the new Progressive Party and supported the presidential campaign of Theodore Roosevelt.
In 1912, Addams published "A New Conscience and Ancient Evil", about prostitution. This book was extremely popular because it was published during the moral panic over "white slavery" (forced prostitution). Addams believed that prostitution was a result of kidnapping only. Her book later inspired Stella Wynne Herron's 1916 short story Shoes, which Lois Weber adapted into a groundbreaking 1916 film of the same name.