Speaking of cowboy culture, here’s a chart of the murder rate in the US for most of the twentieth century.1
Douglas Eckberg presents the revised series because the early Census data under-reported homicides and didn’t cover the whole US; Eckberg’s estimates probably provide a more accurate picture of the murderous early c20.
The numbers indicate something long remarked on but little explained. Here’s Richard Hofstadter in his introduction to American Violence:
For the long span from about 1938 to the mid-1960’s, despite the external violence of World War II and the Korean War, the internal life of the country was unusually free of violent episodes. Industrial violence and lynching had almost disappeared. Rioting in the cities—despite the Harlem riot of 1935, the Detroit riot of 1943, and the Los Angeles zoot-suit riot of the same year—occurred less often than in many past periods. Americans who came of age during and after the 1930’s found it easy to forget how violent a people their forebears had been.
Later in the chapter, Hofstadter speculates as to why the US has a history of violence but little memory of it:
… one is impressed that most American violence—and this also illuminates its relationship to state power—has been initiated with a “conservative” bias. It has been unleashed against abolitionists, Catholics, radicals, workers and labor organizers, Negroes, Orientals, and other ethnic or racial or ideological minorities, and has been used ostensibly to protect the American, the Southern, the white Protestant, or simply the established middle-class way of life and morals. A high proportion of our violent actions has thus come from the top dogs or the middle dogs. Such has been the character of most mob and vigilante movements. This may help to explain why so little of it has been used against state authority, and why in turn it has been so easily and indulgently forgotten. Our new concern about violence today is, among other things, a response to a sharp increase in its volume, but it is also a response to its shifting role. Violence has now become, to a degree unprecedented in the United States, the outgrowth of forcible acts by dissidents and radicals who are expressing hostility to middle-class ways and to established power.
Hofstadter was writing in 1970, when he observed and worried about increased enthusiasm for violence on the left. I do not think this lasted much longer than 1970, yet the murder rate stayed pretty high afterward.
1From Historical Statistics of the US, series Ec190-191.