The U.S. Department of Justice has approved the merger of the world's biggest concert promoter and the world's biggest ticket-seller.

The DOJ's review of the proposed merger between Live Nation Inc. and Ticketmaster Entertainment Inc. was closely watched as a potential bellwether of the Obama administration's antitrust enforcement policies. Antitrust watchers considered the case telling because it involved a vertical merger. Vertical mergers are generally challenged less often, because it is more difficult to show that competition would diminish when merging companies operate at different stages in the supply chain.