Period films work hard to draw us into their vanished worlds—authentic costumes and props, locations free of cellphone towers or jet trails. In “The Guardians,” an uncommonly beautiful drama by Xavier Beauvois, work itself is a strong part of the fascination.
The story unfolds at a measured pace in France, during World War I, on a family farm where women are the guardians of the land and its traditions, while men are being slaughtered in insane, incessant conflict. (A few soldiers come back briefly on leave.) What these women...