On the Fact that (According to Economic Historians, Burton Folsom, Thomas DiLorenzo, and Dominick Armentano) Even Though the Textbook Definition of a Monopoly Specifies that a Particular Business Restrict its Production In an Effort to Jack Up its Prices, the Industries that the Sherman Antitrust Law Targeted for Prosecution In the Late 19th Century Actually GREW at a Rate Six Times that of the Economy as a Whole and AND Their Prices Fell at a Rate Greater than that of the Overall Consumer Price Index

So, no, they weren't true monopolies and the only reason for their prosecution was the disgusting collusion between the companies that couldn't compete due to inefficiency and their political cronies whose palms they greased creating such a policy. A resurgence of mercantilism, in other words.