His industry paved America, quite literally. He took control of his company to provide the railroad companies with steel. With that steel, railroads were built across America which helped Carnegie as well. Those railroads made with his steel provided his with transportation to get his steel across the country quickly to sell more.
There were no rules when Carnegie was building his company. Minimum wages were not established yet nor was the regulation of working conditions. He provided that bare minimum for his workers to insure that he was using everything in his power to gain power.
In addition, he established the "Carnegie Corporation." The charity tries to spread knowledge and understanding of the business world.
Carnegie's business changed the urban world. With his steel, skyscrapers were able to be constructed and more business are now able to thrive.