These changes affected the United States in numerous ways. They affected the economy of the US and the relationships between employers and workers.
These changes affected the economy of the US mainly by creating huge companies that came to dominate the economy. The huge companies also create vast networks that changed what was available to American consumers. For example, they made railroad travel much more possible. They also made the transportation of goods over long distances much easier, thus allowing average people to have access to things that they had not previously been able to get. These large companies often came to have rather contentious relations with their employees. Mass production and the large size of the companies helped to create conditions in which employees felt they were being abused by their employers. They felt that they were being exploited and treated like unimportant cogs in giant corporate machines. This helped to lead to labor strife during much of this time period.
Thus, the increasing size and automation of the large companies had major impacts on the US.