Pre-World War II

Many parties in the second half of the nineteenth century described themselves as social democratic, such as the German Allgemeiner Deutscher Arbeiterverein and the Sozialdemokratische Arbeiterpartei (which merged to form the Sozialdemokratische Partei Deutschlands), the British Social Democratic Federation and the Russian Social Democratic Labour Party. In most cases these parties were avowedly revolutionary socialist, seeking not only to introduce socialism, but also to introduce democracy into nations lacking democratic institutions. Most of these parties were to some extent influenced by the works of Karl Marx and Friedrich Engels, who were at that time working abroad, inLondon, to influence Continental European politics.

The modern social democratic movement came into being through a break within the socialist movement in the early years of the twentieth century. Speaking broadly, this break can be described as a parting of ways between those who insisted upon political revolution as a precondition for the achievement of socialist goals and those who maintained that a gradual or evolutionary path to socialism was both possible and desirable.^[1] Many related movements, including pacifism, anarchism, and syndicalism, arose at the same time; these ideologies were often promulgated by individuals who split from the preexisting socialist movement, and held a variety of quite different objections to Marxism.

The social democrats, who had created the largest socialist organizations of that era, did not reject Marxism (and in fact claimed to uphold it), but a number of key individuals wanted to reform Marx's arguments in order to promulgate a less hostile criticism of capitalism. They argued that socialism should be achieved through evolution of society rather than revolution. Such views were strongly opposed by the revolutionary socialists, who argued that any attempt to reform capitalism was doomed to fail, for the reformers would be gradually corrupted and eventually turn into capitalists themselves.

Despite their differences, the reformist and revolutionary branches of socialism remained united through the Second Internationale until the outbreak of World War I. A differing view on the legitimacy of the war proved to be the final straw for this tenuous union. The reformist socialists supported their respective national governments in the war, a fact that was seen by the revolutionary socialists as outright treason against theworking class; in other words, the revolutionary socialists believed that this stance betrayed the principle that the workers of all nations should unite in overthrowing capitalism, and decried the fact that usually the lowest classes are the ones sent into the war to fight and die.

Bitter arguments ensued within socialist parties, as for example between Eduard Bernstein, the leading reformist socialist, and Rosa Luxemburg, one of the leading revolutionary socialists within the SPD in Germany. Eventually, after the Russian Revolution of 1917, most of the world's socialist parties fractured. The reformist socialists kept the name social democrats, while many revolutionary socialists began calling themselves communists, and they soon formed the modern Communist movement. These communist parties soon formed an exclusive Third Internationale known globally as the Comintern.

By the 1920s, the doctrinal differences between social democrats and communists of all factions (be they Orthodox Marxists, Bolsheviks, orMensheviks) had solidified. These differences only became more dramatic as the years passed.