Social Democracy in The Communist Manifesto.

Karl Marx and Friedrich Engels writing in 1848 about the formation of trade unions and how they would evolve into working-class political parties:

"Thereupon, the workers begin to form combinations (Trades' Unions) against the bourgeois; they club together in order to keep up the rate of wages; they found permanent associations in order to make provision beforehand for these occasional revolts. Here and there, the contest breaks out into riots.
"Now and then the workers are victorious, but only for a time. The real fruit of their battles lies, not in the immediate result, but in the ever expanding union of the workers. This union is helped on by the improved means of communication that are created by modern industry, and that place the workers of different localities in contact with one another. It was just this contact that was needed to centralise the numerous local struggles, all of the same character, into one national struggle between classes. But every class struggle is a political struggle. And that union, to attain which the burghers of the Middle Ages, with their miserable highways, required centuries, the modern proletarian, thanks to railways, achieve in a few years.
"This organisation of the proletarians into a class, and, consequently into a political party, is continually being upset again by the competition between the workers themselves. But it ever rises up again, stronger, firmer, mightier. It compels legislative recognition of particular interests of the workers, by taking advantage of the divisions among the bourgeoisie itself. Thus, the ten-hours' bill in England was carried." (here)

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Britannica Library Adults, about the history of the Labour Party (political party, United Kingdom):

"The Labour Party was born at the turn of the 20th century [i.e. some 50 years after the Communist Manifesto was first published] out of the frustration of working-class people at their inability to field parliamentary candidates through the Liberal Party, which at that time was the dominant social-reform party in Britain. In 1900 the Trades Union Congress (the national federation of British trade unions) cooperated with the Independent Labour Party (founded in 1893) to establish a Labour Representation Committee, which took the name Labour Party in 1906. The early Labour Party lacked a nationwide mass membership or organization; up to 1914 it made progress chiefly through an informal agreement with the Liberals not to run candidates against each other wherever possible. After World War I the party made great strides, owing to a number of factors: first, the Liberal Party tore itself apart in a series of factional disputes; second, the 1918 Representation of the People Act extended the electoral franchise to all males aged 21 or older and to women aged 30 or older; and third, in 1918 Labour reconstituted itself as a formally socialist party with a democratic constitution and a national structure". (paywalled, but see also here and here)

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A similar story applies to the Social Democratic Party of Germany (SPD):

"The SPD traces its origins to the merger in 1875 [i.e. some 30 years after the Communist Manifesto's publication] of the General German Workers' Union, led by Ferdinand Lassalle, and the Social Democratic Workers' Party, headed by August Bebel and Wilhelm Liebknecht. In 1890 it adopted its current name, the Social Democratic Party of Germany. The party's early history was characterized by frequent and intense internal conflicts between so-called revisionists and orthodox Marxists and by persecution by the German government and its chancellor, Otto von Bismarck."

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Pretty much like Marx and Engels wrote, decades in advance.

True, this kind of parties have changed since their origins (and, ab ovo, were vitiated by reformist. moderated, "pragmatist" elements, greatly aided -- I must add -- by academics); true, even the gains achieved were temporary and in the long-run costly in terms of political mobilization.

Still, in that passage of the Manifesto you see the working class struggles evolving from individual workers to small associations to national labour federations (facilitated by modern technology: railways); from labour federations to political parties: political struggle carried on by labour institutions, resulting in regulations shaping the distribution of resources to the workers' benefit.

To me (and that's me: I'm no big-shot professor) it doesn't sound too shabby, particularly considering that, according to Acemoglu and Robinson (here), and Milanovic (here), Marx ignored institutions, technology, politics, and their impact on the distribution of resources in a society:

"We argue that all of these general laws are unhelpful as a guide to understand the past or predict the future, because they ignore the central role of political and economic institutions in shaping the evolution of technology and the distribution of resources in a Society".

But, whatever Marx and Engels wrote, they must be wrong. After all, professors and academics -- whose livelihoods depend on your well-being, surely? -- say so. Trust these people: you'll do just fine. Right?