> Four should be the basis of antitrust policy. Less than four, and there are two options - break up, or become a regulated public utility.
3 options; usually monopolies are matched by regulatory constraints making competition expensive. Removing the barriers to other firms entering the market is always an option.
I'm not sure of many, if any, monopolies where regulatory constraints are the cause. Especially compared to causes like network effects. Do you have a modern example?
I can think of a couple of examples where regulations exist to manage other constraints on competition, like the FCC regulating the spectrum. But not where the regulations cause the number of major competitors to decrease dramatically.
One example I like is Internet Explorer. IE had a "monopoly" back in the early 2000s and made up something like 90% of the browser market. Then Firefox came along and broke the market open, then Google and Apple rolled in like bulldozers [0] and we got to a healthy 4-player market.
Everywhere except for South Korea. You can still read articles on it to this day [1]. Regulations had an unfortunate interaction that made IE into the only option and set up an actual monopoly situation.
The caveat is I personally think monopoly is called far too quickly; as far as I can tell every successful product is a monopoly to someone on HN. A lot of the things people want to call monopolies aren't, they are markets like the browser market that haven't finished settling. Unfortunately they can become ossified due to bad regulatory practice.
[0] What Steve Jobs did to Flash should come with 18+ violence content warnings. They were the days. Nothing could be done about that scourge until suddenly something had been done.
IE didn't lose in the market when Firefox came along. IE lost when the government fined Microsoft billions of dollars and forced it to relinquish it's monopoly position.
Meanwhile the current market is Chrome, reskinned Chrome and Safari. Hardly a healthy marketplace.
3 options; usually monopolies are matched by regulatory constraints making competition expensive. Removing the barriers to other firms entering the market is always an option.