Liz Weis cites:
"It's an awful example, but "a group forming specifically to clean
up a town" might refer to the KKK in The Birth of a Nation."
That, though, is tied pretty closely to the Little Colonel as a motivating
force. Nonetheless, there is a long tradition of such groups in pulp fiction
(if you'll excuse the term) and comics--Doc Savage, the Justice Society of
America, and so on.