Frederick Engels and Karl Marx were the two founders of scientific socialism. About this there can be no doubt. No one can deny that Marx and Engels together developed the social science known as Marxism.
Engels died in 1895, 12 years after the death of Marx. In commemorating this 100th anniversary year, we must ask what Engels' special contribution in the development of a scientific approach to socialism was.
A unique collaboration
As Marx's collaborator, Engels worked closely and intimately with him on all aspects of the class struggle in the historical evolution of capitalism. Engels always denied that his contributions to the development of scientific socialism were independent from those of Marx.
There were those in the movement who tried to divide the two, especially after Marx's death. Some completely negated the influence of Engels, while others tried to elevate him somewhat above Marx.
But Engels brushed all this aside and continued to regard himself as a collaborator of Marx. He did not seek to either elevate himself above the relationship or denigrate himself below it. Often a collaboration ends in the most acrimonious relationship, especially in the fields of politics, literature or the arts. A partnership can quickly dissolve into recriminations. But all attempts by various writers to separate Engels from Marx, to set him up as against or above Marx, were none too politely denounced by Engels himself.
Probably the best account of the relationship between Engels and Marx is given in the book Karl Marx--The Story of His Life by Franz Mehring.
Explaining basic Marxism
After Marx died in 1883, Engels concentrated on popularizing basic Marxist doctrine. His pamphlet Socialism: Utopian and Scientific is still the best and clearest exposition of Marxism, and was the most widely circulated of their works in the 19th century.
This pamphlet is based on excerpts from his longer work, Anti-Dühring, one of Engels' truly great contributions and a detailed explanation of dialectical materialism. The book was written in the form of an answer to Professor Eugen Dühring, who, as Engels wrote in an introduction to the pamphlet, "suddenly and rather clamorously announced his conversion to socialism." But, said Engels, the professor "honored Marx by pouring out upon him the full vials of his wrath."
Anti-Dühring is a painstaking reply to each and every one of Dühring's attacks on Marx. At the same time, it clarifies Marx's principles.
Engels is easy to read. His writings are totally devoid of any pretentiousness with regard to the development of Marxist thought. He does not arrogate to himself the full understanding of scientific socialism to the exclusion of all others. He leaves room for development, as a Marxist should. At the same time, he is the defender of Marx, especially in relation to Dühring.
The best evaluation of Engels' work as a Marxist is the book Karl Marx and Friedrich Engels--An Introduction to Their Lives and Work by David Riazanov.
Kautsky and Lassalle
Karl Kautsky tried to establish himself as the principal interpreter of Marx and Engels, even during Engels' lifetime. Engels was known all his life for his excessive modesty about his contributions to Marxism, as often mentioned in Marx's letters to his friends. However, he was repelled by Kautsky's effrontery, and rebuffed him in a letter.
It's good to remember this in connection with Kautsky's later renegacy from Marxism altogether. Kautsky was recognized as the leading theoretician of social democracy, especially in Germany and Austria. It took a revolutionary of no less standing than V.I. Lenin to take on Kautsky successfully.
Another important figure in the socialist movement at the time of Marx and Engels was Ferdinand Lassalle. He passed himself off as a Marxist, but with his own "improvements," which agitated both Marx and Engels.
Lassalle made some overtures to Otto von Bismarck, the German Chancellor, presumably to advance the cause of the workers while knowing how to deal with class enemies. But Marx and Engels were dubious about whether his maneuvers were principled in character and would be understood by the workers.
Bismarck represented the old feudal ruling classes, notwithstanding the development of the bourgeoisie as the supreme class in Germany. Lassalle's aim, presumably, was to utilize Bismarck against the bourgeoisie, which of course is the principal antagonist of the working class. But in the course of doing so, he compromised the cause of the workers by allying himself with Bismarck.
In the struggle against the bourgeoisie, it must not be forgotten that the representatives of the feudal aristocracy were in no way friendlier to the working class, notwithstanding certain appeals they made to the workers.
Lassalle was very popular among the workers, but his popularity was not because he understood or explained clearly the relationship between the feudal aristocracy and the bourgeoisie. His maneuvers with Bismarck tended to obscure rather than clarify the character of the class struggle in Germany at the time.
Lassalle's death in a duel did not bring a great deal of sadness to Marx and Engels. They felt he was distorting and vulgarizing the struggle against the bourgeoisie by maneuvering with Bismarck. Lassalle's pretensions to Marxism made it difficult for Marx and Engels, especially when their exile from Germany impeded clarifying their relations with him.
Marx and Engels, on the other hand, promoted the working-class struggle independently of alien classes.