It's a film about collective guilt and that uncanny, ungraspable, selfish tendency passive humans have to profit from the misery of the victim, caused by a proactive assailant (the Nazis) who in the film don't even figure. To a point that both profiteers and assailants are put on the same moral plane. The black smoke at the end of the film evokes that same smoke billowing from the crematoriums of the concentration camps, hovering over the conscience of the villagers.