Comedy series in United States were started as early as in 1920s with the introduction of silent movies and later the success of radio stations. Such comedians as Laurel and Hardy, Marx Brothers, Harold Lloyd, Roscoe Arbuckle or Charlie Chaplin were stars of early motion picture industry filming sometimes even few short movies monthly playing the same set of characters. Radio comedy shows that started in 1920s were often based on the vaudeville and burlesque show that audience knew from the theaters. The classic American sitcoms started in 1930s when the plots linked the skits and sketches in whole stories.
The modern American sitcoms started in 1950s with the populatization of television with such titles as I Love Lucy or The George Burns & Gracie Allen Show. Since then most of the American comedy series are kept in similiar - rather family shows targeted for young people and middle-aged audience. Second important factor is influence of stand-up comedy tradition that wasn’t that popular anywhere else in the world.