“Monopoly” basically means a company owns one sector and sniffles any other company getting involved. In the early 1900s, Standard Oil used to own 90% of the country’s gas and oil distribution. Now basically many of those descendants had merged and some sold to global entities.
By the 1950s, the American Telephone and Telegraph company owned 90% of the US telephone lines and interconnects. AT&T was the Department of Justice’s top enemy. That same decade, they were ordered to sell off their Canadian and Asian arm; and in 1956, they were ordered not go into the data processing business (“computers”) despite Bell Labs inventing the transistor that would be the key component in all computers by the 1960s.