Economic growth and the rise of corporations
Saw huge growth after civil war: 40,000 miles of track 1830-70, 110,000 in next 20 years. First transcontinental railroad completed in 1869, there were 5 by 1900.
Were private companies, but growth was facilitated by massive land grants from fed gov (up to 240,000 square miles which could be sold off to settlers when complete). Led to introduction of common time zones across the USA in 1883 and were indirectly responsible for the development of a transcontinental telegraph system, whose stations followed the railroads.