It was getting close to midnight at the Slanted Door, Charles Phan’s renowned Vietnamese restaurant in the Ferry Building, overlooking San Francisco Bay. Outside, Teslas and Priuses were making their way along I-80, over the bridge toward Oakland and Berkeley; a few lights from the tankers, trawling the waters past Yerba Buena Island, flickered like fireflies. A cold early-October breeze rippled the waves.

C.E.O.’s are an early-waking group, and inside the restaurant only a few stragglers remained from the speakers’ dinner of Vanity Fair’s third annual New Establishment Summit. Bob Iger and Richard Plepler had left at least an hour earlier. Sarah Jessica Parker and Jony Ive were gone, too. Meanwhile, the restaurant staff was carefully bustling around the sleek, modernist dining room, whisking away wineglasses and stacking empty dessert plates after another busy night in America’s idea capital.

For some, though, the night was still young. At a long table sat Travis Kalanick, then still the C.E.O. of Uber, and Jeff Bezos, soon to be the richest man in the world (for about four hours, before relinquishing the title back to Bill Gates), who were laughing like old friends despite the fact that they had met for the first time earlier that evening. From a nearby booth, I was struck by how friendly the billionaires seemed with each other. As Bezos howled in his signature laugh, I leaned over to a colleague and whispered about the irony of the conversation. By that time, Uber was already morphing from a ride-hailing service to a massive logistics conglomerate—and emerging competitor to U.P.S., FedEx, and, yes, Amazon. And Amazon was itself far along into its journey of entering new markets (food, Hollywood) and quickly dominating them—an economic earthquake that has become known as the Amazon Effect. The two men may have been laughing that evening, but their companies were on a collision course. In a few years, they would almost certainly be trying to put each other out of business—if they weren’t already doing so secretly. I had no doubt that Bezos and Kalanick, beneath their jovial guffaws, knew that, too.

To be fair to Kalanick, Bezos could have been sitting next to any C.E.O. in the world, and I would have uttered that very same pronouncement. Uber, at some $70 billion in private valuation, is massive. Amazon, however, is gigantic. The company, along with Apple, Alphabet (Google’s parent company), and Facebook, is quickly becoming one of the four horsemen of the economic apocalypse—public companies that are expected to be worth $1 trillion, and continue to reorder the business universe in their image. We’re almost there: Amazon, Alphabet, Apple, and Facebook together are now worth about $2.5 trillion, or about 13 percent of the value of the entire Fortune 500—and growing. Amazon’s stock price has tripled since 2015; Apple is currently storing some $260 billion in cash; Google, as one executive once told me, “has an algorithm that prints money’’; and a quarter of the entire planet is on Facebook. But what’s most remarkable, or terrifying, is that no business is safe from their jaws.

When the meal-kit delivery service Blue Apron announced it was going public, for instance, its bankers had planned to price its initial public shares between $15 and $17. But upon the mere news that Amazon had concocted a pithy slogan—“We do the prep. You be the chef.”—for a potential future meal-delivery business of its own, Blue Apron was forced to slash the share price to between $10 and $11. Earlier this year, supermarket chains saw their market capitalization recede by $22 billion in a mass sell-off just hours after Amazon had announced that it was buying Whole Foods. Presumably, these investors had nightmares of owning shares of the next Borders, which is out of business, or Barnes & Noble, which saw its stock drop some 75 percent in the past two years alone.