The 1920s is the first decade whose style and tastes seem to represent a clear internationally-recognisable break with what had gone before, though elements (Hollywood, jazz, women's emancipation) predated it. The 1930s has a distinct character too, though the 40s might be seen as two halves, one continuing the 30s, the other merging with the early 50s (the same might indeed be said of the 50s and 60s too). The turn of the century had earlier been seen too as marking a new era, though the style and art of the 1900s seem to follow a pattern set in the 1890s. The rise of such rapidly-moving international tastes seems associated with the development of mass media - first an illustrated press and advertising, later cinema, broadcasting and recorded music. But it's been with us for a long while.

The 1890s are the earliest that seem to have been considered to have had a distinct character - by the 1920s they were called the "Naughty Nineties" in Britain and the "Gay Nineties" in America, stereotyped for both sexual scandals and decadence as well as a supposed pre-1920s innocence.