The period from 1870 to 1900 saw rapid urbanization in the United States, driven by industrialization and immigration. Cities like New York, Chicago, and Philadelphia grew dramatically as the urban population tripled from 10 to 30 million. This era of growth brought significant challenges, including overcrowding, poor sanitation, and labor unrest. In response, the Progressive movement emerged, pushing for social and political reforms to address urban issues and improve living conditions for city dwellers.