I think that the advent of technology has fueled Postmodernism. The growing use of technology to simultaneously expand and shrink our world is something that drives Postmodernism. Consider that the use of television is a force that can bring more information about the world to the individual. Yet, at the same time, it can also be used as a way to decrease connection to the world, as the individual can only relate to the world through television. One can substitute the internet for television and see the same experience. Postmodern thinkers would point to this as one reality that has helped to transform the world and one's thinking of it. This is less about being "good" or beneficial as much as it is technology impacting our own perception about being in the world.
Another transformative experience that the Postmodern would point to would be the increased globalization of the world. It is one in which cultural distinctions are rapidly disappearing. In its place is a realm where individuals have to accept that literally anything is possible. For thinkers like Havel, this condition is what has both caused and defined Postmodernism:
For me, a symbol of that state is a Bedouin mounted on a camel and clad in traditional robes under which he is wearing jeans, with a transistor radio in his hands and an ad for Coca-Cola on the camel's back... I see it rather as a typical expression of this multicultural era, a signal that an amalgamation of cultures is taking place. I see it as proof that something is happening, something is being born, that we are in a phase when one age is succeeding another, when everything is possible. Yes, everything is possible, because our civilization does not have its own unified style, its own spirit, its own aesthetic.
It is in this vein, one in which there is a lack of unity and a lack of a "unified style," that has caused Postmodernism. Havel and other Postmodern thinkers point to such a reality as one in which individuals must demonstrate readiness to embrace a new condition. It is one that is in stark difference to what has already been understood because it lacks totality. In this, Postmodernism has been created and existed.