Omnicom announced on Wednesday its long-awaited $13 billion acquisition of rival Interpublic Group (IPG) has finally closed, following regulatory approval in Europe.Why it matters: The deal creates the largest ad holding group globally and is likely to usher in more consolidation in an era defined by scale, data and AI. Driving the news: The all-stock deal gives Omnicom shareholders 60.6% of the combined company and IPG shareholders' 39.4%. The combined company will now trade under the ticker OMC on the New York Stock Exchange."With the completion of the deal, Omnicom is setting a new standard for modern marketing and sales leadership," CEO John Wren said in a statement.The big picture: The deal underscores the pressures in the ad industry and need for industry consolidation.With IPG, Omnicom can make bigger platform investments, secure more major commercial deals, deepen generative AI partnerships and strengthen its creative talent.Catch up quick: The European Commission approved the deal on Sunday without any conditions, saying it raised no competition concerns in Europe. The UK's Competition and Markets Authority greenlit the acquisition in August, also without any conditions. The other side: Across the Atlantic, U.S. regulators have been slightly more demanding. The Federal Trade Commission in June said it will approve the mega-merger, but only if the agencies agree they won't bar ads based on politics. State of play: Omnicom's deal is the latest in a sweeping reorganization of the ad industry. Agencies are adapting to the rise of generative AI, self-serve ad buying platforms and other tech changes.Legacy holding companies are collapsing brands. WPP, which prior to this merger was the largest ad group by revenue, merged its creative agencies and rebranded its media arm. Private equity has been actively acquiring and helping modernize smaller agencies. IPG previously sold two agencies to PE firms — R/GA to Truelink Capital and Huge to AEA. Last week, ZMC-backed agency Wpromote acquired Giant Spoon.WPP's U.S.-listed shares soared earlier this month following reports of takeover interest from smaller French agency Havas and PE firms.