Documentary maker Barbara Kopple lived with coal miners’ families for a year in order to make this startling, far-reaching film, which uses a desperate localised strike – called by workers seeking union recognition – to examine the way America treats its poor. Alongside vivid footage of a conflict spiralling out of control, she examines corruption and compromise within the union, the duplicity and heartlessness of the coal companies, and the impossible odds stacked against the workers, in the shape of a police force, legislature and judiciary all conspiring to keep them under foot.

Impassioned, committed but also willing to acknowledge the complexities of the situation and the personal shortcomings of some campaigners, it’s ultimately a valuable, inspiring and upsetting film, a hymn to the virtues of authentic unionisation, when America still had such a thing. For an outside observer, it also highlights just how damaging US firearms laws are in a situation like this, making the escalation from placid to dangerous all the steeper – and infinitely more destructive. And Kooper soundtracks the whole thing with a succession of beguiling, soot-choked renditions of bluegrass songs about mining, some done professionally, others sung with an overpowering intensity by minor players in the film.