Postmodern literature is a form of literature that is characterized by the use of metafiction, unreliable narration, self-reflexivity, and intertextuality, and which often thematizes both historical and political issues. This style of experimental literature emerged strongly in the United States in the 1960s through the writings of authors such as Kurt Vonnegut, Thomas Pynchon, William Gaddis, Philip K. Dick, Kathy Acker, and John Barth. Postmodernists often challenge authorities, which has been seen as a symptom of the fact that this style of literature first emerged in the context of political tendencies in the 1960s. This inspiration is, among other things, seen through how postmodern literature is highly self-reflexive about the political issues it speaks to.