In the late 1800s, businesses had gotten to be very big and very consolidated in the United States. The country was industrializing and becoming more connected and huge businesses were becoming more feasible. This led to a situation in which firms like Standard Oil came to hold monopoly power over certain areas of the economy. People felt that the firms were abusing their power and there was something of an outcry against them. This came first from the populists in the 1870s and 1880s and then from the progressives in the early 1900s.
There were two things that the Congress did to respond to these critics. First, it enacted some regulations of these businesses. The major example was the Interstate Commerce Act of 1887. This allowed the government to regulate the rates that railroads charged for transporting cargo. These laws were meant to prevent some monopolies, at least, from abusing their power.
Second, the Congress created laws that were specifically meant to curb or to ban monopolies. The first of these was the Sherman Antitrust Act of 1890. This ostensibly made it illegal for an individual to monopolize or attempt to monopolize a market. It also made combinations or contracts “in restraint of trade” illegal. This law was not terribly effective and so Congress created the Clayton Antitrust Act of 1914 to more clearly specify what was illegal.
Thus, Congress responded by trying to stop some of the negative effects of monopolies and by trying to simply ban monopolies.