BlackRock, Vanguard, and the Return of the Trust

What a monopoly actually is

A monopoly is a market with one seller.

Not a big company. Not a company you dislike. The word has a technical meaning: a single firm supplies a market, and because buyers have nowhere else to go, that firm sets the price rather than accepting one. Economists call the second part market power — the ability to raise price above what competition would allow and lose too few customers to care.

That definition matters, because it is the one the law uses, and because it is the reason the obvious objection to this piece exists. BlackRock does not sell you an airline seat. Vanguard does not refine your gasoline. Neither is the only seller of anything. On the strict definition, neither is a monopoly, and anyone who knows the term can say so in one sentence.

Hold that objection. The law is broader than the word — and the thing the law was actually built to destroy was not a monopoly at all. It was a trust.

The laws written to break them

American antitrust law was built in a thirty-year span, against a specific enemy: the trust — an arrangement where the shares of competing companies were placed in the hands of a common set of trustees, who then ran the competitors in concert. Not a merger. Common ownership.

The Sherman Act (1890) made it a federal crime to enter "every contract, combination, or conspiracy in restraint of trade," and separately banned "monopolization, attempted monopolization, or conspiracy or combination to monopolize." It still carries criminal penalties: corporate fines up to $100 million, personal fines up to $1 million, and up to ten years in prison.

In 1911 the Supreme Court used it. Standard Oil Co. of New Jersey v. United States ordered the Standard Oil trust dissolved, and it was broken into 34 separate companies. Descendants of those pieces are still trading today — ExxonMobil among them.

The Clayton Act (1914) was passed because the Sherman Act had proved too slow. It targets conduct before it produces a monopoly, and its Section 7 is the provision this article turns on. It prohibits a firm from acquiring "the whole or any part" of another company's stock where the effect "may be substantially to lessen competition, or to tend to create a monopoly."

Read that carefully. Not creates a monopoly. May be substantially to lessen competition. Congress chose that wording deliberately — it wanted probabilities, not certainties, and it wanted stock acquisitions specifically. The same Act separately bans interlocking directorates: the same person sitting on the boards of competitors.

The Federal Trade Commission Act (1914) created a standing agency and banned "unfair methods of competition" as a category, so that new arrangements would not need a new statute each time.

Three laws, one target. The concern was never company size as such. It was competitors who stop competing because the same people own them.

The argument

Look again at the chart at the top of this page, and at two rows in particular.

BlackRock discloses 6.6% of Delta Air Lines. BlackRock discloses 6.6% of United Airlines. Delta and United compete for the same passengers on the same routes. The identical figure is not a coincidence of rounding; it is what happens when a firm holds the whole index rather than a view about either airline.

Now ask the question the Clayton Act asks. Not "is BlackRock the only seller of flights" — it sells none. The statutory question is whether acquiring stock in competing firms may be substantially to lessen competition.

There is a mechanism, and it is not subtle. A manager holding a large position in every airline does not profit from a price war between two of them. A fare war transfers money from one holding to another and destroys some on the way. The manager need not instruct anyone. It needs only to be an owner whose interest in Delta beating United is, uniquely among Delta's owners, close to zero. Executive pay tied to industry performance rather than company performance does the rest.

This is not a fringe reading. In 2016 the Harvard Law Review published Einer Elhauge's "Horizontal Shareholding," which argues that stock acquisitions creating anticompetitive horizontal shareholdings are already illegal under existing antitrust law, and calls for enforcement actions to unwind them. In 2018 the Journal of Finance published Azar, Schmalz and Tecu's study of exactly the airline case above, estimating that common ownership of this kind is associated with ticket prices between 3% and 11% higher than separate ownership would produce.

Then there is scale. BlackRock reported $14.0 trillion under management at the end of 2025. Vanguard manages roughly $11.6 trillion. Between them that is more money than the annual economic output of any country on earth except the United States, and it is invested, by design, across every large public company at once.

The trust that the Sherman Act was written to break placed competing companies under common owners. That is a description of the chart on this page. The difference is one of scale and of intent — Standard Oil's trustees meant to control the oil market, while an index fund means only to track an index. The Clayton Act does not ask about intent. It asks about effect.

What the other side says, because it is not nothing

Three objections deserve to be stated properly.

The money is not theirs. Index funds hold shares for millions of ordinary savers — pensions, retirement accounts, teachers and mechanics. "BlackRock owns 6.6% of Delta" is loose; BlackRock manages that stake. The people who own it are scattered and mostly unaware. But they do not vote it. BlackRock does. Ownership is diffuse; the vote is concentrated, and the vote is the lever antitrust law has always cared about.

The funds are passive. They cannot sell a badly run company that stays in the index, so the usual discipline of a shareholder is unavailable. That is true, and it cuts both ways: an owner who cannot sell has only voice left, and these firms exercise it — voting on every director at thousands of companies every year.

The evidence is contested. It genuinely is. The airline finding has been challenged on its methodology, and economists continue to argue over whether the effect is real and how large. That argument is live, and this article does not settle it.

But notice what survives all three objections. The structure is not in dispute. Every figure on this page comes from the companies' own filings. Nobody disputes that the same handful of managers are the largest shareholders of firms that compete with each other. The dispute is only about what follows from it.

Why the word still fits

Return to the definition. A monopoly is a single seller with power over a market.

These firms are not sellers. They are something the 1890 Congress would have recognised faster than we do: a common set of owners standing behind competitors who are supposed to be fighting each other. That is the arrangement the antitrust laws were written to end — the trust, reassembled out of index funds instead of trust certificates, and assembled so gradually, and for such unobjectionable reasons, that no one had to decide to build it.

Whether it is a monopoly in the dictionary sense is a question about vocabulary. Whether it is what the antitrust laws were written to stop is a question about the laws, and on that question the Clayton Act's own words are the strongest argument available: may be substantially to lessen competition.

The evidence for the "may" is on this page. Open any company and see who is above it.

Check it yourself

Every number in the chart links to the filing it came from. The laws are short and readable: the Sherman Act is 15 U.S.C. §§ 1–2, the Clayton Act's stock-acquisition provision is 15 U.S.C. § 18. The Harvard Law Review article is public. So are the proxy statements.

Nothing here requires you to take anyone's word for it, and you should not.