The Weather Underground documentary is about the radical left-wing militant organisation with the same name which was active from 1969-1977.
The 2002 film which was narrated by actress Lili Taylor (The Conjuring) depicts the rise and fall of this radical organisation. Starting out under the name "Weathermen", The Weather Underground Organization (WUO) formed at the University of Michigan with the goal of spreading in popularity and taking over the US government in a revolution. Some of the main principals of the group were communism, black power and opposition to the Vietnam War which were often campaigned with violence.
Through the 1970's WUO became infamous for destructing property by bombings, while nobody was killed in any of these attacks, three members were killed by the Greenwich Village townhouse explosion in 1970.
After the Vietnam War ended in 1973, the group gradually declined in popularity over the following few years before disbanding in 1977. The WUO is one of the most notorious revolutionary youth movements of all time, and it is feared a similar movement could rise again in the US with similar hard left-wing principals.