Stalin’s Curse: Battling for Communism in War and Cold War. By Robert Gellately. Knopf; 464 pages; $32.50. Oxford University Press; £20. Buy from Amazon.com; Amazon.co.uk

FIRST and foremost, Stalin was a communist, who believed that the sacred cause justified the most extreme measures: what non-believers would call unparalleled barbarity. This central message in Robert Gellately’s masterly new book is an uncomfortable one for those who believe that Stalinism was an aberration, or a reaction to mistakes made by the West. It is facile to say Stalin was simply a psychopath, that he believed in terror for terror’s sake, or that the Red Tsar’s personality cult replaced ideology. A Leninist to his core, he was conspiratorial, lethal, cynical and utterly convinced of his own rightness.

“Stalin’s Curse” draws mainly on German and Russian archives, plus numerous first-hand accounts, and the author’s formidable interpretative skills. Unlike other biographies that have focused on the most sensational episodes in the dictator’s life, it sets Stalin firmly in the historical context: the rise (and eventual fall) of what the author calls the “Red Empire”.

Mr Gellately’s latest work has a good claim to be the best single-volume account of the darkest period in Russian history. It is part of a crop of excellent new accounts of the era. It sits well with Timothy Snyder’s 2010 book, “Bloodlands” (about mass killings) and Anne Applebaum’s “Iron Curtain” (which deals with eastern Europe after 1944 and which came out last year). It is also a worthy successor to his “Lenin, Stalin, Hitler: The Age of Social Catastrophe” (2008), which compared and contrasted the three monsters.

Stalin’s supposed strategic genius gets short shrift, along with his generalship. Because communist doctrine said all imperialists were equal, Stalin failed to see that the Western powers were not the same as Nazi Germany, and might even be useful allies against it. For all his paranoia and cynicism, the Soviet leader was determinedly friendly to Adolf Hitler, apparently believing that close ties with the Soviet Union made a Nazi attack less likely. But Hitler saw it the other way round: relying on Soviet imports endangered his long-term goal of destroying communism.

Where Stalin excelled, again and again, was in ruthlessness and attention to detail. He paid minute attention to extending Soviet rule in places conquered at the war’s end. He took great interest in details of science and cultural policy, fearing even the faintest breach in communist omniscience. The results might be disastrous: but they were in accordance with communist theory, which was what mattered.

Mr Gellately, a professor in Florida, has a deft touch with detail. For all the havoc he wreaked on the countryside, Stalin knew next to nothing about it (he seems to have visited farms only once, in 1928). During their furious conquest of Germany, the Red Army soldiers avenged their homeland’s suffering in an orgy of destruction. An eyewitness describes their taking “axes to armchairs, sofas, tables and stools, even baby carriages”. Individual stories are recounted with understated sympathy. But the scope of the suffering is inconceivable. An all but forgotten post-war famine in the Soviet Union killed 1m-2m people. Communism probably killed around 25m: roughly the same toll of death and destruction as that wrought by the Nazis.

Aside from the chief villain, Western leaders too come in for quiet but deserved scorn. Both Franklin Roosevelt and Harry Truman failed to grasp their counterpart’s malevolence. Winston Churchill made casual deals that consigned millions of people to slavery and torment. The foreigners thought Stalin was a curmudgeonly ally to be coaxed and cajoled. He treated them as enemies to be outwitted. Far from provoking Stalin into unnecessary hostility, the Western powers were not nearly tough enough.

Some of the strongest passages of the book concern Stalin’s final years: the sharpening contrast between his obsessive paranoia and his analytical powers; the looming anti-Semitism, and the beginnings of a massive new arms build-up. Little of that came to fruition, sparing the world untold new horrors. But what Stalin did achieve was quite bad enough.