oftentimes, mergers can make markets less competitive, and this harms consumers by reducing choice and increasing prices. When a merger is announced, federal and state authorities "review" the merger very carefully to make sure competition is not reduced. For example, federal and state authorities may look at how much of a market the merged company will control, and if the merged company will result in less competition nationally, within a specific state, or even within a specific city. If federal or state authorities think a merger may reduce competition and harm consumers, they may ask the merged company to sell parts of the company to a competitor (just to keep the market competitive). Sometimes, federal or state authorities can sue to stop or reverse a merger.

There seems to be a lot of mergers in the news lately (e.g., media companies, airlines). Is there a rationale for why the Antitrust Division of the Department of Justice allows these companies to merge to get even bigger?