UnitedHealth Group didn't even announce its acquisition last week of PreferredOne, the health insurance unit of Fairview Health. A colleague reported the story based on a state regulatory filing.

Fairview dropped a figure of "north of" $100 million to size the deal, although that includes capital Fairview was able to pull out of PreferredOne. So it's not exactly the purchase price.

It's clearly a big deal to Fairview, a $6 billion operation. But it was "immaterial," as the accountants say, to UnitedHealth. Not big enough for the company to talk about. And good luck spotting it in the numbers in the next quarterly filing.

UnitedHealth Group, of Minnetonka, was a startup back in 1977. Today it's value in the stock market is roughly $400 billion.

UnitedHealth didn't get big by out-inventing the competition, although getting to the top of a very large industry is a great achievement no matter how it was done. It got there by doing a lot of these PreferredOne kind of deals.

Health insurance was a messy industry in need of consolidation, in part because the states had a big role in regulating health insurance, and UnitedHealth was happy to help clean it up.

The U.S. now has about 900 health insurance providers, according to a firm called ValuePenguin. But UnitedHealth and its four closest competitors in size have nearly half the market. It's not clear who might be left of any meaningful size that the regulators would let any of these leaders buy.

It might seem like a remarkable thing — all this consolidation — but it turns out that pretty much all industries go through it. The classic business school framework is a four-stage process and the domestic health insurance industry seems to be headed for the last stage.

For some businesses it's hard to even imagine they could ever have been run out of a founder's garage. If you hear the word Detroit, you might think of a U.S. auto industry crushed by its bureaucracy. But Detroit the city was the Silicon Valley of the early 20th century.

It was teeming with entrepreneurs inventing things, hyping unworkable prototypes, rounding up investors and so on.

A famous lawsuit seems emblematic of that early era, pitting Henry Ford against his partners, the Dodge brothers. Henry Ford cited lofty principles when he refused to pay a Ford Motor Co. dividend, but he mostly wanted to keep the money out of the Dodge brothers' competing car company.

Industries grow up when somebody emerges to take charge, buying up the also-rans and forging an ever more formidable competitor.

In the U.S. automotive business that was Alfred P. Sloan Jr., Ford's rival and the longtime president of General Motors Corp. Sloan was a manager, not an inventor, and his achievement was creating a modern corporation.

Today, companies with at least 10,000 workers employ a much bigger percentage of all workers than they did 30 years ago and have more Americans working for them now than all the companies with 50 or fewer employees.

Industry after industry has consolidated, and an open market advocacy group showed that that just two companies had grown to own more than half their markets in many of them.

You couldn't help but hear about skyrocketing lumber prices earlier this year. Industry concentration might explain some of that. In the production of a building-products staple called oriented strand board, or OSB, the top two firms now have 44 % of the North American market and the top five have roughly 70 %.

In media, Google's parent Alphabet, Amazon.com and Facebook just reached a milestone of industry concentration when the three of them together last year collected more than half of all advertising spending in the country.

All this is of interest now because a new era seems to be dawning in antitrust enforcement under the new Biden administration.

The last great burst of this took place in the 1970s, and one of the highest-profile cases involved the breakfast cereal business and General Mills. The top firms were found to have had a vastly dominant share of the market, with pricing power and the ability to keep upstarts at bay.

The government's case eventually failed. One problem with anti-trust enforcement is that the proposed solution is often busting up the company, as was the case here in breakfast the cereal industry. We might've had Cheerios Corp. of Golden Valley set up to compete against the Count Chocula Co. of Hopkins.

It's not easy to imagine how someone would break apart a company like Google today, other than by breaking off YouTube, and it's hard to cheer for that kind of big government intervention. What would be better are measures that would encourage new market entrants.

And that's one reason to cheer for electric vehicle maker Tesla, even though you may not love Tesla CEO Elon Musk.

You often hear Tesla described as disruptive, but that's simply wrong. A disruptive business is an upstart that undercuts the big guys in a market by serving the customers that are "overserved" by the established players.

Truly disruptive startups sell something that looks a lot worse, with a lot less functionality, to customers happy enough with the lower performance if they can buy it a lot cheaper. In time the start-ups can grow and knock the legs out from under the established players.

Tesla's first big seller, the Model S sedan, can sell for up to $140,000. Mercedes or BMW owners weren't overserved customers who bought a Model S because it was so much cheaper and simpler. They were buying largely the same thing, only a better version.

The point of all this is that Musk is trying to beat the likes of BMW, Toyota, Volkswagen and GM by doing it the hard way. Given their size, brand power, distribution reach and automotive know-how, the game should be over by now and Tesla long gone from the board.

And yet Musk is winning.