1940s

One of the sub-genres that defined classic American crime and detective movies was film noir, a style that was pervasive in detective films of the 1940s and 1950s. Film noir arose during the post-World War II period in the United States as a generation that fought in one of the most brutal conflicts the world had ever seen returned home to a changed America where jobs were scarce and the national mood seemed darker and more cynical than during the war itself. 

Film noir is not easily defined. The actual words come from French and mean "black cinema." It was in France during the post-war years that the term was used to describe a certain set of Hollywood films that were saturated with a darkness and cynicism that was not seen before.