Definition
Progressivism was an American reform tradition active roughly from the 1890s to the 1920s that sought to clean up urban politics, regulate concentrated economic power, professionalize government, and apply scientific expertise to social problems. It cut across both parties and produced direct primaries, the federal income tax, women's suffrage, food-and-drug safety regulation, and the civil-service ethic that government employment should be based on merit rather than party loyalty.
For The Power Broker progressivism is the world Robert Moses entered as a young man — Oxford-educated, Bureau-of-Municipal-Research idealistic, fluent in the language of "good government" that became, in his hands, an instrument for accumulating bad government.
Why it matters
How it works
A progressive program in city government has three legs: professionalize the workforce (civil-service exams, defined careers), make decisions transparent (public budgets, hearings, recorded votes), and apply technical expertise to social problems (sanitation, public health, traffic engineering). The bet is that better procedures and better people will produce better outcomes.
The bet's weakness is that procedural cleanliness and technical expertise can be captured by a single individual with greater administrative skill than anyone watching. Progressivism gave Moses the language and the legitimacy; he supplied a will to power its founders had not anticipated. The result is a cautionary tale about reform traditions whose institutions outlive the people who designed them.