In 1842 the most advanced industrial city on earth had no adequate account of itself. Manchester ran the world's cotton, and the science that claimed to explain it — political economy — could derive prices, rents and wages as if they were weather. It had nothing to say about the cellars. Into that gap walked a twenty-two-year-old. His father had sent him over to learn the trade at the family firm, Ermen & Engels; he spent the better part of two years walking the districts instead. What Friedrich Engels brought back was the claim that the misery was not a defect in the machine but the way the machine worked.
He had already turned on his own class once. The son of a pietist textile manufacturer in Barmen, a mill town in the Wupper valley, he was pulled out of school at sixteen, a year short of the Abitur, the school-leaving examination, and put into a commercial apprenticeship in Bremen. At eighteen, writing under a pseudonym, he published Letters from Wuppertal — an account of the mill hands in his father's valley, and of the religion that told them to bear it. Before he had read a line of communist theory he had chosen his subject: the human cost of a particular factory system, described by someone who knew where the ledgers were kept.
The Condition of the Working Class in England appeared in 1845, in German, for Germans; English readers waited forty-two years for a translation. Its method was both the scandal and the achievement. He went in block by block, court by court, cross-checking what he saw against parliamentary reports and against the Chartists, the mass movement for the working-class vote, and the Owenites, the cooperative socialists who followed Robert Owen, who let him in. Mary Burns, the Manchester working woman who became his companion, is generally credited with opening those doors; the record does not say how much of the route was hers, and honest biographers stop there. The argument outran the reporting: trade crises were not accidents but a rhythm the system required, and they would deepen.
A year earlier he had written Outlines of a Critique of Political Economy, fifteen pages that treated competition and private property as the thing that needed explaining, not as the given from which everything else is explained. Marx read it and turned to economics. The partnership everyone remembers as senior and junior began with the junior man handing over the subject.
After the 1848 revolutions collapsed he went back to the Manchester office he despised and stayed twenty years, clerking cotton to keep the Marx household solvent, retiring only in 1870. The theory that made him famous was funded by the trade it condemned.
What he wrote after retiring shaped how the world received the theory. Anti-Dühring (1878), aimed at Eugen Dühring, a Berlin lecturer with a rival socialism, turned a polemic into the first connected statement of the doctrine, and the pamphlet carved out of it, Socialism: Utopian and Scientific, became the text through which most people who ever encountered Marxism encountered it. He extended the dialectic from history into nature. He assembled the second and third volumes of Capital out of unfinished manuscripts, in 1885 and 1894.
Whether that systematizing preserved Marx's thought or hardened it into something Marx never held is a genuine and unsettled quarrel. Engels himself, in his last years, wrote that neither he nor Marx had ever claimed economics was the only force in history.