How did the Second Industrial Revolution affect the United States?
It helped the USA become the world first economic power
The second industrial revolution was characterized by a development of the steel industry and of the railways. Chemical industry also emerged. This enabled the USA to become one of the major economic powers in the world and the first worldwide after WWI.
It meant people continued to migrate from the countryside to the cities and people in Europe moved the USA to find employment in factories in big cities such as Boston or New York. Socially speaking it meant tensions emerged, a good example could be the 1877 strike which started in Pennsylvania or the workers killed in Haymarket in 1886 in Chicago during a protest for a eight-hour day.
The building of the railroads also played a major role in the conquest of the west after the Civil War.