How did the expansion of railroads affect commerce?

Made trade MUCH MUCH EASIER and more profitable. Resulted in business having more power along with pendleton act. Sped up industrialization/westward expansion. Brought wealth to many towns through which railroads passed. Look up long/short haul rates and Cornelius Vanderbilt
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It helped to promote economic growth. If you're a farmer that needs to sell his product out of the middle of nowhere, where he lives, you need a way to get your product to market. Or if you're a mining company, you need a way to get your coal sold to other companies. Railroads in the 1800s provided the answer for many people that wanted to sell commodities, such as vegetables, fruits, and meat, as well as non-food items like barbed wire, coal, and wood.