The Black Legion is noteworthy not only as an indictment of hate groups in America, but also as one of the first films to feature Humphrey Bogart in a leading role.
Frank Taylor (Humphrey Bogart) is a blue-collar worker at a factory somewhere in the midwestern United States, with a loving wife (Erin O'Brien-Moore) and young son (it was rare for Bogart to ever portray a family man on-screen), and a couple of close buddies. Taylor thinks he's a shoe-in for a promotion to foreman, but the position goes to someone else: Joe Dombrowski (Henry Brandon), a Polish-American immigrant, on account of Dombrowski discovering a way to improve efficiency. Taking advantage of Taylor's resentment, one of Taylor's co-workers (Joe Sawyer) recommends that Taylor join The Black Legion, which markets itself as anti-foreigner. Buying into their hateful rhetoric, Taylor joins up, and the Legion burns down Dombrowski's house and farm, driving him and his family out of town. Dombrowski's disappearance means that the foreman gig is Taylor's for the taking.