Narrator: Listen to part of a lecture in a history class.

Professor: Okay. So we've been talking about various factors that have changed the United States's economy. And one especially important factor was the development of railroads.

When the railroad system expanded throughout most of the United States, it fundamentally changed the way business was done in this country.

For one thing, expansion of the railroads enabled companies to start selling their goods all across the country. Since trains could now transport merchandise all over the United States, companies could now sell goods to consumers pretty much anywhere in the country.

For example, there was a big company that sold clocks. The company started in a big city.

And before the development of the railroads, the company could only sell its clocks to people who lived in or near that city. But when the railroads expanded, the company could loaded its clocks on the trains and have them delivered to all parts of the country.

Railroads also changed business in the U.S. by making it possible to open factories in new locations.

Many factories had machines that were powered by certain raw materials, like coal. And railroads made it possible to transport those raw materials to areas of the country where they weren't found naturally.

A good example is some factories in the southern United States. In certain parts of the south, there wasn't much naturally-occurring coal.

So before the expansion of the railroads, there weren't many factories there, because there were no raw materials like coal to provide power for the factories’ machines.

But after railroad lines were built in the south, coal could be brought in from other parts of the country. So new factories were able to open there.