Thanks again for the detailed response. Oligopoly was a new word for me. I can see that it's more or less the same as a monopoly, but it's just when a small group of companies have "monopoly" over a market, rather than just one. You talk about governments enabling collusion. How does this happen? Aren't there actually laws against price collusion? I think your farm example. That does make sense to me. Why wouldn't that be possible in today's market? On the other hand, a road as long as your farm land may not be that useful. People would still have to continue on the other road. The big company could just not build on-ramps and off-ramps to the farmers road. They'd also have to have a tolling system that could cut that portion of the roads out of what the drivers pay.
Governments enable collusion, especially in the US, by making entry into a market more difficult. Either through regulations, permits, expensive legal hoops to jump through, etc.
Imagine you have a car design that is better and cheaper than all current cars sold. You build the car in your garage and want to start selling and scaling up to full production of these cars. Do you really think you could just set up a factory and start selling them? No. The amount of regulations required to become a car manufacturer is insane. It's almost as if the 3 or 4 auto manufacturers in the country are paying politicians or something. Tesla tried to do it on their own but had to play ball and pay off the government to get to the point of being able to sell cars.
Almost every other industry has permits, required certifications and schooling, etc. These are not for any useful purpose other than keeping out competition.
I currently live in French Polynesia where there are only 3 banks. No new banks can be created due to the amount of regulation requirements to open one. So the 3 banks set the prices on various things very high. It costs about 20% to exchange dollars to francs. And of course, only the banks are allowed to exchange currencies due to government regulations. If there were no government intrusion into money exchanges you'd have people at the airport charging 2-3% just standing there waiting as people get off the plane. You'd have your taxi driver exchanging cash for you. I'd be able to set up a bitcoin exchange here, an ATM at the airport. But it's not allowed.