The bid business transformed the US in various forms. It created new social classes - wealthy industrialists, middle classes and blue collar working class -.
Factories needed labor force, so immigrants from Europe went to the US looking for work, also Americans that used to live in rural areas moved to the cities to work.
The problem for workers was that they were mostly unemployed a part of the years, the wages were low and labor unions were not supported by the government and the owners of the factories who wanted big profit.