Answer:
The second industrial revolution began whith the adoption of new steel production techniques. Thanks to these techniques, steel became cheaper more widely adopted.
Railroads began to be made of steel instead of iron. Because steel is a much more powerful material, rails now lasted for longer periods of time and were more powerful. This sparked the introduction of railroads, first in the United Kingdom, and then in the United States.
Railroads became the most important source of transportation, both of passengers and materials. In the U.S. the railroad network was extensive and allowed the shipping of goods from coast to coast. This meant increases in productivity and capital that could be reinvested in the adoption of new technologies, forming a virtuous cycle.