Final answer:
Karl Marx would refer to the DuPonts, Vanderbilts, and Rockefellers as 'capitalists' or 'bourgeoisie', highlighting their wealth and role in capitalist society.
Step-by-step explanation:
Karl Marx would likely have used the term capitalists or bourgeoisie to describe industrial magnates like the DuPonts, Vanderbilts, Rockefellers, and other major industrialists in American history.
These individuals, who amassed great wealth and power during the Industrial Revolution, embodied the capitalist class that Marx argued exploited the working class (proletariat) for their own gain.
He would probably critique their roles in perpetuating the capitalist system and the inequalities that came with it, particularly their practices of monopolization and exploitation of workers.