It depends on how one defines monopoly. The U.S. has been pretty permissive of corporate agglomerations since 1985 or so (1984 being when A&T was split up). If it were up to me, I'd take a somewhat more critical eye to them. It being theoretically possible for a competitor to emerge doesn't mean you aren't a monopoly if it's very unlikely any could actually succeed in practice.
So let's go down the list...
Not really applicable:
- Sports. Major League Baseball is a sanctioned monopoly in the U.S.; I'm not as sure about other sports leagues. But this is sanctioned, like the Postal Service or Systembolaget, and not necessarily a bad thing.
- Some Internet Service Providers/cable companies. They often have local monopolies. If they have forced their competitors out locally and refuse to allow other companies to use their infrastructure, the cost of a new entrant to the market is very capital-intensive, and the existing monopolist could always price below market rates until the new competitor goes out of business, subsidizing their losses via other markets. This should be more heavily regulated, and localities should always be able to deploy municipal broadband (some states currently ban this).
- Google. Effectively a monopoly in Internet search and video content, to a similar degree to Microsoft in operating systems in the '90s. And like Microsoft did then, Google abuses their dominant position in one market to the detriment of competitors in other markets. Use Google Search, they push GMail. Use YouTube, they push Chrome. Use Chrome, they push all their other services, and collect more data to enhance their search engine. You never *have* to use it, but it always "works best" with other Google products, and they aren't shy about reminding you. They've already been fined billions by the EU over these practices. And that's all without mentioning Android...
- Amazon. A classic bundling across multiple industries to stifle competition. Online ordering of nearly everything, and it's not rare for them to be effectively the only supplier (online or local) for some goods. Warehousing to fulfill those orders. Delivery trucks to deliver them. Additional content (video, music, etc.) bundled with their Prime membership. Access to all the data from online ordering, that no one else has, to enhance the warehousing operation. Ability to ban third party merchants from their marketplace if they perceive them to have any advantage over Amazon itself (and it's been fairly widely reported to happen). Arbitrariness at best towards the third-party delivery contractors they use (and whom they've increasingly forced out of business). If Microsoft should have been broken up into multiple companies in the '90s, Amazon deserves so at least as much today.
In certain areas/ask again in 2024:
- Apple. In terms of software distribution on their platform, I think there's a good case to say "yes". No one else can compete on iOS, and they take a 30% share. But not on the overall phone or computer markets. To me, the software distribution monopoly *should* count, but this might require legislative changes.
- Disney. Gaining a concerning amount of media market share; further acquisitions should be prevented.
- Cellular phone providers in the U.S. They rarely have the regional monopolies that ISPs do, but have consolidated down to three major providers and one notable regional one (U.S. Cellular). MRVNOs lessen the argument for monopoly status, but nonetheless, the concentration is concerning. Further mergers should not be permitted, or we may wind up with early '80s AT&T again.
- Twitter. They're a new distribution format. Some places use them. Some use Facebook. Some use e-mail. Some use Instagram. There doesn't seem to be that much consolidation here, at least compared to others mentioned.
- Walmart. Yes, they're big. But so is Target, and Kroger. There was once a fear that they'd monopolize all of retail, but that hasn't really been progressing for a while.
- TSMC. They aren't the only top-end fab. Samsung also operates top-end fabs in significant quantities, and Intel is getting back on their feet as a third after having stumbled in the late 2010s. The concentration of the semiconductor industry both from an industry standpoint, and a geographic one, is a cause for concern, and further aggregation should be limited; I can see the argument for "yes" here. But as seen by Global Foundries (the 4th top-end fab a few years ago) deciding to stick to 12nm and smaller, extreme capital costs limit how many companies can effectively operate in this space.
- Steam/Valve pre-Epic. Yes, it did look like it might wind up that way for a while. But it wound up being more early mover advantage. They bet on the right horse (digital distribution) earlier than nearly everyone else, and few competitors emerged because it was still much cheaper than the old physical distribution. But there always were some competitors - GOG, Gamersgate AB from Sweden (still in business), Impulse from Michigan (which was doing okay until Gamestop bought them), EA's Origin, Itch.io. And as far as I am aware, the closest Steam ever came to abusing their monopoly was allowing developers to optionally integrate with Steam Achievements and Multiplayer. I don't believe they ever required anyone to distribute exclusively via Steam to distribute via Steam at all, though due to convenience many chose to do so. Please feel free to provide a link to documentation otherwise if it exists - I didn't check Gamasutra every day so I may have missed something.
As seen by the "ask again in 2024" category and a couple of the "No" having previously been "ask again in 2 years", I also would favor investigations in cases where it's not clear cut, but a risk. The DOJ's settlement with Microsoft, including 6 years of closely monitored probation, was fairly effective at making Microsoft think twice about monopolistic abuses, even if it didn't prevent them from adding the web browser to their categories dominated in the late 1990s. And thus, while you could still argue their desktop operating system market share, and perhaps their office suite market share, is de facto a monopoly, the threat posed by it no longer appears to be very great in comparison to several other companies.
Microsoft's Windows market share monopoly also illustrates a conundrum - even if you split up Microsoft tomorrow, you couldn't legislate your way to a viable Windows competitor (except perhaps by also forcing Apple to license macOS for non-Apple computers). Thus, it's important to try to intervene before such dominance is established. But even in cases where such dominance as Windows' is the case - YouTube and Google Search being additional examples - preventing a company from having multiple of them still reduces the impact of the monopoly.
The South Korean chaebols are another interesting case, where I would not be surprised if some South Koreans would argue that they have effective national monopolies in certain industries. Samsung, Hyundai (which does way more than just cars), LG, there's a few others that are not as internationally well-known.