The film is set in a post-apocalyptic and neo-Western version of the disestablished United States in the then near-future year of 2013, sixteen- plus years after unspecified apocalyptic events, starting with the breakdown of society through “hate crimes and racially motivated attacks (by) a militia- like group” the same as the Ku Klux Klan led by Nathan Holn, progressing to war, followed by plagues, that collectively left a huge impact on human civilization and erased most technology.

References:
https://en.wikipedia.org/wiki/The_Postman_(film)