This massive saga about Finnish immigrants in early 20th-century America combines fascinating detail with overlong narration. Karl Marlantes’s previous novel, 2010’s Matterhorn, and his crushing memoir, What It Is Like to Go to War, explored his experiences as an officer in Vietnam; they were the work of a reflective, hugely brave and – by necessity – ruthless soldier. After these existentially wrenching books, he stated he would move away from writing about war. Conflict also drives Deep River, an imposing novel about Finnish immigrants in America, but it is the struggle of Aino Koski, of her brothers and of the emerging American labour movement. There is also the clash of humans with wild nature in the logging and salmon fishing industries of the Pacific Northwest, and the intrinsic conflict of siblings against siblings, and wives against husbands. Inspired by Marlantes’s own family ancestry, Deep River is a massive American saga, a historical epic of documentary detail spread across the early 20th century – and 700 pages. We witness the traumas of Aino as a sort of proto-Rosa Luxemburg, who with her brothers escaped tsarist persecution and deadly poverty in Finland for America. Aino’s brother Matti is a tough, aspiring businessman who embraces the Darwinian crudity of American capitalism; their brother Ilmari builds a church and also explores the lore and spirituality of Native Americans. The themes of idealism, materialism and God, guiding forces of America itself, are personified in this one family. There is also Askel, a childhood friend and fisherman who has a long, complex relationship with Aino. The novel is a stalwart refresher on how tough life must have been when to post two letters on union business cost more than a week’s wages. As well as Aino’s story, this is a chronicle of the “Wobblies”, the Industrial Workers of the World union, in a period when conflict between workers and the status quo in the US was violent and naked. The book’s flaw is not the earnestness of its political story, but its narration. From Robert Graves to Ernst Jünger, James Salter to Michael Herr to Marlantes himself, the horror and fear of combat electrifies the simplest prose with huge tension and brutal significance. In Deep River, little of that gripping intensity is present; extensive sections of a long book feel perfunctory. Marlantes writes almost wholly in accessible, unchallenging prose, pretty much stripped of description: “Rauha’s face settled once again into its cold mask.” Men are “like ants in a vast landscape”. Without the energy and anticipation of a combat scenario behind it, it only has the exhaustive agenda of spelling out every significant event that happens to the Koski siblings. Chapters lack dramatic tension. Impoverished Makki seeks the beautiful Kyllikki as his bride – the affluent parents object, but determined and wily Makki outfoxes them. You see it coming. There is an accumulating sense of documentary-like facts being adumbrated and ticked off, qualified by the helpful dates on which they occurred. Readers are told lots of dry information, rather than being permitted to experience these facts through the story, so we get plain, clunky exposition: “The Swedish-speaking and Finnish-speaking communities kept pretty much to themselves but with written material in both languages becoming common as well as increasing literacy among the younger people, it didn’t surprise her that Askel … ” The logging sequences contain fascinating detail and a lovely set piece when whole residential log huts are loaded by crane on to a train, transported to the next felling zone then offloaded on the rough ground – of course never resting level, so that Aino’s ankles ache from walking uphill within her own house. Marlantes is quite capable of wonderful stuff like this. However, logging is already a rich fictional mini-genre: Annie Proulx’s magnificent Barkskins, Tim Gautreaux’s The Clearing, Ken Kesey’s Sometimes a Great Notion, Robin Jenkins’s The Cone Gatherers, David Adams Richards’s The Friends of Meag er Fortune, Ursula Le Guin’s The Word for World Is Forest. They all leave far more powerful impressions of foresting – or, more accurately, the uneasy emotional impact of deforestation – than Deep River does. We learn and grow from the novel, and many will embrace its long-term company and businesslike storytelling. Through girth and plenitude, hefty books often attempt to grab status. Marlantes is far too sincere a writer to be accused of that; yet I believe a shorter book might have given this story so much more power. . Alan Warner’s next novel, Kitchenly 434, will be published in 2020. Deep River is published by Atlantic (£17.99). To order a copy go to guardianbookshop.com or call 020-3176 3837. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.