The Weather Underground was a far-left Marxist militant organization first active in 1969, founded on the Ann Arbor campus of the University of Michigan. Originally known as the Weathermen, the group was organized as a faction of Students for a Democratic Society (SDS) national leadership. Officially known as the Weather Underground Organization (WUO) beginning in 1970, the group's express political goal was to create a revolutionary party to overthrow the United States government, which WUO believed to be imperialist.
https://en.wikipedia.org/wiki/Weather_Underground