SUBDUED for years after the financial crisis, mergers and acquisitions came roaring back as companies seek to boost revenue at a time when sluggish economic growth and low inflation make that difficult.

    Companies around the world struck US$4.6 trillion worth of takeovers in 2015, edging out 2007 to be the biggest year ever for such combinations, according to Dealogic. U.S. corporations led the charge, inking US$2.3 trillion in deals, also a record.

    There is another number that perhaps best captures the moment: 58. That is how many mergers topped US$10 billion, well ahead of the prior high of 43 in 2006.

    The corporate marriages could have a significant impact because most involve firms in the same industry combining. That stands in contrast to the private equity takeovers of the last merger boom — deals that generally didn’t involve merging rivals in the same sector of business — and the technology acquisitions from the one before that, which were paid for in many cases with stock that proved to be overvalued.

    Major sections of the U.S. economy are set to be reshaped, assuming regulators don’t stand in the way. The government recently moved to block retailer Staples Inc.’s proposed acquisition of Office Depot Inc. and General Electric Co.’s sale of its appliance unit to Electrolux AB.

    Some of these mergers could be a way station to yet another move. In health care, Pfizer Inc., maker of staples including Lipitor cholesterol pills and Advil pain medication, said it would swallow Botox maker Allergan PLC for about US$150 billion. But the deal may soon be followed by a breakup that would create major new players in the drug industry.

    Meantime, chemical and agricultural products giants Dow Chemical Co. and DuPont Co. said they would merge to form a company worth about US$120 billion — but then break into three new firms.

    In the biggest deal ever for makers of semiconductors, the ubiquitous engines of technological progress, Avago Technologies Ltd. plans to buy Broadcom Corp. for US$37 billion.

    “This year may well be the start of a major restructuring of corporate America as it seeks to compete in the new economic environment,” said Frank Aquila, a senior partner at law firm Sullivan & Cromwell LLP.

    For many employees, the restructurings could be painful. Mergers often bring layoffs to help pay for the transactions.

    Headed for their worst performance since at least 2011, U.S. stocks haven’t lacked for drama. The Dow Jones Industrial Average, down 3.9 percent so far this year, set half a dozen records in the first half, as an expanding U.S. economy and expansive Federal Reserve policy helped build on large gains in 2013 and 2014.

    But spring optimism gave way to anxiety. Weakening global growth highlighted the risk of a sharp slowdown in China, which shocked the markets by devaluing its currency in August. Major U.S. stock indexes suffered their largest declines since the euro crisis, capped by an Aug. 24 rout that featured trading halts in hundreds of exchange-traded funds, raising fresh questions about the integrity of the U.S. market structure and the impact of high-frequency traders.

    Shares largely recovered, but a new threat emerged: a steep decline in the prices of junk bonds. On top of that, the Federal Reserve’s move to raise interest rates tightens financial conditions. Rarely has a flat market year felt so topsy-turvy. (SD-Agencies)