From its beginnings in eighteenth-century London, this is the history of the largest urban police departments in the United States and a social portrait of America during the first century of its existence. From the birth of the New York City Police Department in 1845 to the end of World War II, each city had its share of crime, murders, vice, drug dealers, and addicts.

Boston, New York, Chicago, Philadelphia, San Francisco, and Los Angeles each had their own history and developed in different ways according to local realities. But in every case, each police department had to deal with its share of good and bad cops, Pinkertons, gangsters, revolutionists, politicians, reporters, muckrakers, arsonists, murderers, district attorneys, strikers, labour spies, hanging judges, and axe-swinging crusaders, as well as every conceivable element of American society high and low.

But American Police also offers a view of the FBI and its legendary director, J. Edgar Hoover; District Attorney Earl Warren and police commissioners such as Teddy Roosevelt, Stephen J. O'Meara, Richard Enright, Grover Whalen, Louis J. Valentine, and August Vollmer; and tough cops like Captain William"Clubber" Williams, Johnny "the Boff" Broderick, and John Cordes.

It is also the history of crime over the course of a century that transformed the United States from a former colony of the British Empire to a powerful and restless nation poised for spectacular growth.