In recent years, large American corporations have been on a buying spree. Amazon bought Whole Foods in 2017. That same year, CVS announced it would acquire the health insurer Aetna. AT&T finally acquired Time Warner in 2018 after a two-year delay. Meanwhile, Silicon Valley's giant technology companies have come to play a dominant role in almost everyone's life. American corporations seem to be bigger and more powerful than ever, and some researchers have begun to worry that a lack of competition is holding back innovation and depressing wages.
Are markets in the United States more concentrated today than they were a decade ago? This is a surprisingly difficult question to answer. Markets change quickly so there is no obvious way to compare markets over time. Some markets around now are entirely new, while others that would have been around ten years ago have disappeared. But we can still get some idea of the general trend by looking at datasets that record the size and dominance of firms over time. There are not many of these datasets, but one good one is the US Census Bureau's Economic Census.