Sentence:  And it is clearly argued by Lord Percy of Newcastle , in his remarkable long essay , The Heresy of Democracy , and in a more general way by Voegelin , in his New Science of Politics , that this same Rousseauan idea , descending through European democracy , is the source of Marx 's theory of the <WSD>dictatorship</WSD> of the proletariat . 
Meaning of the word marked with <WSD> tags:  a form of government in which the ruler is an absolute dictator (not restricted by a constitution or laws or opposition etc.)