"Vanguardism" is a concept that has its roots in Marx's and Engels' emphasis on the necessity of a political party that plays a leading role in the workers' movement — the "advanced guard" or "avante-guard" from which the word "vanguard" derives. This teaching of Marx and Engels was re-affirmed by the 1891 "Erfurt Programme" of the German SPD, and disseminated across the globe in large part thanks to Karl Kautsky's book "The Class Struggle". Suffice to say, Karl Kautsky was not commonly referred to as the "Pope of Marxism" for no reason. These ideas were highly influential on the young Vladimir Ilyich Ulyanov — aka "Lenin" — who successfully put them into practice in Russia in his founding of the Russian Social Democratic Labour Party, and later the Bolshevik party. While much of the international socialist movement had descended into opportunism and support for their own national states and bourgeoisie after the outbreak of the First World War, Lenin and the Bolsheviks — along with other leading communist figures like Karl Liebknecht and Rosa Luxemburg in Germany — held steadfast to the orthodox Marxist principles that has widely been betrayed (even by Karl Kautsky who Lenin now denounced as a "renegade"). Nevertheless, in the aftermath of the Russian Revolution the genuine international Marxist movement was reforged with the founding of the Communist International, and the lessons of Marxism and Bolshevism on the question of the party were re-affirmed and once again widely spread. The communist movement, under Lenin and the Bolsheviks' leadership, resolved once and for all to split from the Social Democratic parties which had now become infested with opportunism, support for imperialism, and bourgeois/petit-bourgeois distortions of Marxism. To stand for an independent, revolutionary organisation free from such problematic influences was the watchword of the day, with the concept of the "vanguard" party reaching its highest level of development.
Note: Slight mistake at 03:21. The USSR did not technically exist until its founding in 1922. At the time the party was simply called the "Russian Communist Party", not the CPSU.
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