Monopolies are not always illegal, though. What actions have to be taken to make a monopoly illegal? What are the courts and the Department of Justice looking for when they accuse a company of an illegal monopoly?

You bring up an interesting concept and that is the concept of horizontal division of markets. Can you expand on what this concept is and how it applies to our given scenario? (Sherman Act, Rule of reason & Per Se Rule)

I think it can be easy for many people to forget (if they even know) that AT&T had a monopoly as a telephone company that was forced to split in 1984, creating several smaller companies, but effectively breaking up the monopoly they had held with regards to the phone services offered. Because of this monopoly, I think it is one of the reasons that the Justice Department is always quite leery of any mergers that involve AT&T. Below is an interesting article about the break-up and the pros and cons of the split. Your thoughts?

Beattie, A. (2021, May 7, updated). AT&T's successful spinoffs. The breakup of Ma Bell. Investopedia. https://www.investopedia.com/ask/answers/09/att-breakup-spinoff.asp