Born in 1876,Weimar-era gay publisher and activist Friedrich Radszuweit joined public gay life in 1923, when he founded the Bund für Menschenrecht (Federation for Human Rights, or BfM) in Berlin and began publishing dozens of gay, lesbian, and trans*-themed periodicals. The BfM grew to become the largest (indeed in some sense the only) mass-membership LGBT organization of its time. It claimed 100,000 members. Too bad its founder would end up advocating for collaboration with the Nazis.
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SOURCES:
Beachy, Robert. Gay Berlin: Birthplace of a Modern Identity. New York: Vintage Books, 2015.
Halifax, Noel. "Richard Linsert and the First Sexual Liberation Movement." http://socialistreview.org.uk/420/richard-linsert-and-first-sexual-liberation-movement
Marhoeffer, Laurie. Sex and the Weimar Republic: German Homosexual Emancipation and the Rise of the Nazis. Toronto: University of Toronto Press, 2015.
Miller, Ben. "Friedrich Radszuweit and the False Security of Collaboration." http://outhistory.org/blog/in-the-archives-friedrich-radszuweit-and-the-false-security-of-collaboration/