Market power often comes from genuine innovations, efficient business models and the creation of stuff that consumers like, but it also has costs for society. Those costs are outlined in the classic theory of monopoly. Without competition, companies can increase their prices to maximize profits. As prices for products rise, many consumers can't afford them, and so the monopolistic company reduces what it produces and sells. And that means they need fewer workers.

If it were just one company, it wouldn't be such a big deal for the overall economy. But Eeckhout documents an astonishing rise of market power across all sorts of industries since 1980. We're not just talking about the usual suspects here: Amazon, Google, Facebook and so on. We're talking about everything from the makers of cat food to the sellers of caskets. More than half of all the dry cat food in the United States is sold by one company. Almost 90% of mayonnaise in the U.S. is sold by two companies. Airlines, social media, pacemakers, pharmaceuticals, energy, cars, home improvement — there are so many industries that are increasingly dominated by only a few companies.