Why were some men called robber barons?

The term "robber barons" refers to men who amassed considerable wealth through morally reprehensible means. They are of two types: the medieval European lords who charged inflated tolls for passage through their lands or waterways, and the 19th-century American capitalists who monopolized businesses through robbery, extortion and corruption.

A standard definition for “robber” is a person who seizes something from someone else through force or violence, while a “baron” is a member of the nobility or someone with great power. Thus, the term “robber baron” was devised to reflect the feelings of the exploited underlings, and its meaning is scornful.