Karl Marx's audience refers to the various groups of people, particularly the working class and intellectuals, whom he aimed to reach with his revolutionary ideas during the Second Industrial Revolution. His writings, especially 'The Communist Manifesto' and 'Das Kapital', were designed to inspire the proletariat to recognize their exploitation and unite against the bourgeoisie. This audience was critical in the context of rapid industrialization, social upheaval, and economic inequality that characterized this period.