Take, for instance, the article “Hungary” of 1849, published in the Neue Rheinische Zeitung, the German newspaper of which Marx was then editor. It was written by Engels under Marx’s direction, and it advocates the “total extinction” of “ethnic trash”. It concludes: “The next world war will cause not only reactionary classes and dynasties, but entire reactionary peoples to disappear from the earth. That too is progress.”

This justification of genocide was republished in 1913 and so has been known for more than a century — yet Marxists ignore this and other texts that might reveal their hero’s feet of clay. During the 1930s, indeed, Stalin became so alarmed about the damaging material that might emerge from the complete edition of Marx and Engels then being prepared in Moscow that he had its editors liquidated.

One reason why Marx did not care how many individuals, classes or peoples were sacrificed on the altar of revolution is that he believed in historical determinism. In 1871 he encouraged the Paris Commune (which was led not by Marxists but more moderate socialists), watched in grim satisfaction as its supporters were slaughtered by the forced of the Third Republic, and mythologised the whole episode into a communist uprising. Violence was inevitable — and anyway the revolution required martyrs.

Another reason for his ruthlessness is that he never bothered to understand how wealth is created. Marx’s theory ignores the prosperity generated by free markets or the benefits of private property. He denied the contribution made by the middle class (or “bourgeoisie”) to the unprecedented riches of Victorian society, insisting that their profits consisted of “surplus value”, labour stolen from the working class (or “proletariat”). Marx stuck rigidly to the idea that value was created solely by labour — an idea that was refuted in his lifetime by economists such as Menger, Jevons and Walras. Marx never understood the role of markets in determining the price of both goods and labour.

Marx was also certain that if the rich got richer, the poor would get poorer, by a process he called “immiseration”. Eventually, the whole capitalist system would collapse — and the most advanced industrial economy would be the first to do so. In the 19th century, that meant Britain. As he toiled away on his magnum opus in the then new Round Reading Room of the British Museum, a British revolution seemed to Marx inevitable. Though he never used the word “capitalism” in Das Kapital, he looked forward to its downfall. The proletariat, led by the party, would take over the means of production from the hated bourgeoisie. Finally, the state would “wither away”.

What happened was the opposite. As the rich got richer, the poor got better-off too. By the time the first volume of Das Kapital appeared in 1867, it was obvious that Victorian England was in no danger of revolution. The working class was more prosperous than ever before, thanks to capitalism. Most were not radicals, either — just the opposite, indeed, because they had too much lose. That year, Benjamin Disraeli, the Conservative Prime Minister, doubled the number of voters with his Second Reform Act. Many turned out to be working-class Tories.