Before serving as mayor, La Guardia represented Manhattan in Congress and on the New York City Board of Alderman. As mayor, during the Great Depression and World War II, La Guardia unified the city's transit system; expanded construction of public housing, playgrounds, parks, and airports; reorganized the New York Police Department; and implemented federal New Deal programs within the city. He pursued a long series of political reforms curbing the power of the powerful Tammany Hall political machine and re-establishing merit-based employment and promotion within city administration.