The 1930s to the 1980s is referred to as the reform era of policing. Why? What r

The 1930s to the 1980s is referred to as the reform era of policing. Why? What reforms were made?
Peak, K. J., & Madensen, T. D. (2020). Introduction to Criminal Justice: Practice and Process
(4th ed.). Los Angeles, CA: SAGE Publications, Inc.