Post modernism came about due to the changing social climate, and the growing multi centralism of the world through global communication and technology. In many ways people believed that the aesthetic quality of society was diminishing. Post modern caused a tsunami of change among popular style and challenged the term modernism as only a continuation of the parent it "rebelled" from.
The designers of the 1970's embraced the term, and the style giving it a strong and popular foothold in society.
Contrary to popular belief Post-Modernism is neither anti-modernist nor retaliation. It accepts the ideas of the twentieth century, and as its name implies it acknowledges the idea of modernism but goes beyond the faction, and blends it with other, newer ideas. It really is in fact just an extension, not a deliberate opposite to the main, creation of the modernistic way of thinking.
Although it was quite a popular wave of thinking, like any trend and all movements of the last two hundreds years, it has also produced its fair share (and perhaps a little more) of bad, tactless art. The prefix "post" has several contradictory hints and insinuations, one of which demonstrates the incessant struggle against stereotypes. The French philosopher Jean-Francois Lyotard has focused completely on the statement "the fetish of the new" concluding that "A work can become modern only if it is first Postmodern". Postmodernism thus understood is not modernism at its end but in nascent state, and this state is constant. Like any cultural movement its defining characteristics have changes shape and meaning since its conception in the late 1950's. Its slight changes in name such as post -Modern, postmodern and Post-Modern Movement have isolated it from other advents such as Pop art and feminism, which took place quite independently, (hence the lack of the word "post").
Post Modernism is sometimes thought of as anything after modernism, but it is hard and selective about the history of the definition "Modern", as the modern movement itself was in fact about other movements, it is a reoccurring trend.