You can do a comparison/contrast of police systems in Australia, United States, and Canada to see how policing evolved from Britain. You have three case studies. You have Canada which has a national police force. You have the United States which but its law enforcement emphasis at the municipal level, in particular the Office of Sheriff. but as law enforcement needs increased in the 20th Century the door was opened to state and federal police agencies. Then there is the Australians who pretty took examples from the Canadian and American systems in their police structure.