What factors combined to make the u. s. a mature industrial society after the civil war?

The factors that helped create a more mature industrial society in the United States following the Civil War were the way people began moving from rural farmlands into major cities, the invention of both the railroad and the telegraph, immigrants coming to the country created a huge labor force, there was a large concentration of economic power by important people like Rockefeller and Andrew Carnegie, and the middle class became more instituted in business as well as mass production as new factories were built.

Not sure this is a hard one huh