AFTER years of post-recession somnolence, corporate takeovers and mergers have ballooned to their highest level since 2007, fueled in part by American companies’ fleeing the United States to save tax dollars.

Gaming the tax system has, of course, long been a popular blood sport for American business, particularly for pharmaceutical concerns and for technology darlings like Apple.

But these days, tax avoidance feels like a full-fledged business strategy, with American citizens as the losers.

At the moment, New York-based Pfizer is battling to acquire the British giant AstraZeneca. At $106 billion, that would be the largest of the current raft of tax-advantaged deals. If it’s completed, Pfizer would become a British company, saving it $1 billion or more annually because of Britain’s lower tax rate (21 percent and soon, 20 percent) and other potential breaks. By comparison, Pfizer is currently taxed at a 27 percent rate. Since 2008, about two dozen American companies have used mergers to shift their legal residence abroad through the process known as inversion. That’s about the same number as over the previous 25 years. All told, the raft of increasingly sophisticated tax-avoidance schemes has helped the share of corporate profits paid in taxes to drop significantly.