Final answer:
Zebulon Brockway, known for supporting indeterminate sentencing, was part of the Progressive era.
Step-by-step explanation:
Zebulon Brockway, a leading advocate of indeterminate sentencing, is associated with the Progressive era. During that time, reformers sought to transform various social institutions, including the prison system.
They aimed to rehabilitate individuals rather than just imprison them, indicating a shift from punitive measures to corrective ones.
The Progressive era was marked by efforts to improve social conditions and to treat social deviants, which included criminals, with the intention of reintegrating them into society as law-abiding citizens.
This era signified the move towards indeterminate sentencing, which allows for the early release of prisoners based on their rehabilitation progress, rather than fixed sentences without consideration for individual circumstances.