Final answer:
Turn-of-the-century political bosses were at the helm of political machines like Tammany Hall, offering services for votes in a system rife with corruption. Progressive Era reforms eventually aimed to curtail their power and clean up politics.
Step-by-step explanation:
The political bosses of turn-of-the-century cities were most often leaders of political machines, which were informal political groups designed to gain and maintain power.
These bosses would provide necessities such as jobs, housing, and protection in exchange for votes, a process often tainted with corruption and bribery. Infamous examples include William Marcy Tweed, known as "Boss" Tweed, of New York's Tammany Hall, whose regime exemplified the corrupt practices of such machines, including election rigging and kickbacks.
Over time, the Progressive Era brought about reform efforts that aimed at reducing the power of political machines through measures like the adoption of the commission system and the city-manager form of government.