Modern mass parties are nearly everywhere in the West the children of the industrial revolution and of the political pressures for popular representation which accompanied it. It was largely through them that ‘modern industrial society … stirred into action those classes which formerly only played a passive part in political life’ (Mannheim, 1941, p. 44). In the study of modern political institutions, the analysis of the role and operation of political parties occupies an ever-increasing place. For the study of the modern socialist movement and for the development of socialist ideology the German Social Democratic Party is also of seminal significance.