On this day in 1956, the People's Movement for the Liberation of Angola (MPLA) was founded in a merger between 2 smaller communist and anti-colonial parties. The MPLA was a major faction in the Angolan Civil War, which lasted until 2002.
Image: An MPLA poster commemorating the organization's anniversary [digitalcommons.colum.edu]
The Society for Human Rights, founded by Henry Gerber on this day in 1924, was the first gay rights organization in the US. A few months later, the org was raided by police and Gerber was subjected to a highly publicized series of trials.