Henry Martinson, an activist for the Socialist Party in the 1900s, then in North Dakota’s more successful Nonpartisan League in the teens, gets his close-up in John Hanson and Rob Nilsson’s “Prairie Trilogy.” Courtesy of Northern Pictures & Citizen Cinema

“I suppose ‘socialist’ was, fifty, sixty years ago, what you would term today an incurable optimist,” declares Henry Martinson, that sunniest of radicals, at the age of 97 in John Hanson and Rob Nilsson’s short portrait Survivor. Martinson certainly got called worse than “optimist” in his decades of organizing farmers and laborers on the high plains of North Dakota, a mission that started in the first years of the twentieth century, as the homesteaders’ sod shanties gave way to farmhouses, and their crops got cynically undervalued by a system of buyers who — in Martinson’s words — “wouldn’t know a goldurn plow from a corn shredder.” First as an activist for the Socialist Party in the 1900s, then in North Dakota’s more successful Nonpartisan League in the teens, Martinson fought the exploitation of local farmers by out-of-state conglomerates.

Hanson and Nilsson’s arresting Prairie Trilogy, a feature-length assemblage of three shorts created in the late 1970s, capture the moment when the history of Dakota socialism was fading from memory, a time when even some of the old-timers who once fought for farmers were now griping about people on welfare. Survivor and Rebel Earth find Martinson — a homesteader, organizer, painter, editor of a socialist paper, and his state’s poet laureate — looking back on a lifetime of pushing for a change that only once seemed like it was truly here, with the 1918 electoral victory of the Nonpartisan League. That triumph gets cast as epochal, even fabulist, in the fleet docu-collage Prairie Fire. The bracing history is narrated by Martinson and features jaunty folky labor songs, a host of archival photos and marvelous propagandistic cartoons (“Things As They Should Be” reads the text above an illustration of a farmer on a throne as businessmen bow), and priceless footage of plains life shot between 1915 and 1921 by Frithjof Holmboe, co-director Nilsson’s grandfather.

Prairie Fire is a hoot, a joy, a thrill, rich with local color and indelible plains photography. Survivor and Rebel Earth, by contrast, are elegiac, but often joyously so. (All three films have been newly restored and are enjoying their first full theatrical release; they are being presented in DCP.) Both find Martinson engaged in that great Midwestern project of “visiting” — sitting around with the people he knows and gabbing about how things were and what they’re becoming. He and the directors tour around the state, by car and train, visiting stores and bars and the capital. The North Dakotans chat and sing; at a party someone busts out a violin; Martinson gives an impromptu socialist speech in an empty state house; as he loses at a round of blackjack, Martinson blisteringly compares the game to capitalism itself. Above all else, they swap stories. One jewel turns on Martinson’s certainty that if the cop who hauled him away during a raid on the Wobblies back in the 1910s had needed to carry Martinson just one more block, the chatty activist might have won him over to the cause.

But he’s upbeat. Chipper Martinson — dubbed “Hip Hop Henry” in one of the tunes Nilsson wrote for these films — promises that, even as America was sliding toward Reaganism, a “socialist regime is as sure to come as daylight comes after dark.” A less sanguine prognosis comes from Hank Kiehn, the former mayor of Minot, North Dakota. “New ones step into what the old-timers and I fought for,” he says, before rattling off a list of the labor movement’s gains over the course of the century: pensions, the forty-hour work week, living wage, vacations with pay, social security. But rather than complaining about how the young people don’t know or appreciate what their forebears achieved, he’s issuing a warning: “If they don’t stay organized, these conservatives are gonna take it away from them.… If you don’t keep fighting, they’re gonna take what little you got away from you.”

Prairie Trilogy

Directed by John Hanson and Rob Nilsson

Northern Pictures & Citizen Cinema

Opens July 27, Metrograph

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