What does it mean to be a socialist in America, and why do people get so angry, and angrily terrified, when some Americans espouse socialism as a fairer system than the one in place? These questions have been coming up more frequently in recent years, prompted by the rhetoric and policy propositions of the recent presidential hopeful Senator Bernie Sanders and the ascendance of younger politicians, including Alexandria Ocasio-Cortez, the congressional candidate from New York who is unabashedly aligned with the Democratic Socialists of America.

You may find an engaging answer to at least the first of the above questions in “Prairie Trilogy,” a collection of three short documentaries made between 1977 and 1980 and directed by the regional filmmakers John Hanson and Rob Nilsson. Now playing in New York in restored form, the movies are companion pieces to Mr. Hanson and Mr. Nilsson’s 1978 feature “Northern Lights,” a fictionalized tale of the real North Dakota labor union called the Nonpartisan League, which formed about a half a decade before America’s involvement in World War I.

The first of the three films is “Prairie Fire,” which uses historical photos and archival footage (shot by Frithjof Holmboe, Mr. Nilsson’s grandfather) to tell the story of a simple struggle in 1916 between the grain farmers of North Dakota and the money men who exploited them.

The narrator is Henry Martinson, 97 at the time this movie was assembled, who speaks of the “Eastern grain markets, railroads and banks” that the Nonpartisan League mobilized against. Martinson was an organizer for the League; before that, he had edited a socialist newspaper called The Iconoclast.