The Impact of UK's Block on Microsoft-Activision Merger.

The U.K.'s Competition and Markets Authority blocked Microsoft's proposed acquisition of Activision Blizzard, citing concerns that the deal would reduce innovation and consumer choice. The decision reflects a broader rethinking of consolidations between firms in a buyer-seller relationship, particularly vertical mergers. Antitrust authorities, in the U.S. in particular, have recently taken a much more hostile stance toward vertical mergers, recognizing that owning a portfolio of products could give a corporation a potent competitive weapon. The FTC and DOJ have an opportunity to build on their enforcement efforts against vertical mergers by announcing bright-line market share tests for mergers in their new guidelines.