What business was the major force behind economic growth and the first big business for the US?

What business was the major force behind economic growth and the first big business for the US?
The first "big businesses" sprang up in the late 1800's with the creation of large trusts in the U.S. These trusts were usually associated with the railroads.

If you're looking for a more in-depth information, I would research these individuals:

1. John D. Rockefeller - Standard Oil

2. James Pierpont Morgan - Banking and Securities

3. Andrew Carnegie - U.S. Steel

4. Cornelius Vanderbilt - Railroad Tycoon

These men were HUGE in the advancement of business and corporate activities in the late 1800's. They each developed extremely large "trusts" that combined multiple businesses into one large corporation or business (what most think of as a monopoly). Formal monopolies were against the law, so tycoons created these trusts to circumvent the law and bend the rules)