Entrepreneurs managed to create large-scale corporate enterprises in the late nineteenth century by using questionable methods to drive their competitors out of business.
At that time, during the so-called Gilded Age, business regulation was virtually nonexistent. As a consequence, wealthy entrepreneurs—known pejoratively as robber barons—were able to use all kinds of sharp practices to increase their wealth and power at the expense of the competition.
Captains of industry like John D. Rockefeller used their extraordinary wealth and power to buy up smaller companies, ensuring that they had no serious competition and could make even bigger profits.
Once such entrepreneurs had driven their competitors out of business, by fair means or foul, they were able to create large-scale corporate enterprises that virtually cornered the market in a variety of industries, most notably steel, oil, and railroads.
The so-called robber barons, following Rockefeller's example, also used novel business arrangements called trusts that involved the combination of the main company—which, in Rockefeller's, case meant Standard Oil—with affiliated companies in order to create a giant corporate entity that would monopolize the provision of the relevant product or service.