The United States attacked first, imposing tariffs on steel and aluminium from around the globe and threatening to hit tens of billions of dollars on Chinese products.
Now, the world is punching back.
The European Union on Friday is to slap tariffs on $US3.4 billion in American products, from whiskey and motorcycles to peanuts and cranberries. India and Turkey have already targeted US products, ranging from rice to autos to sunscreen.
In two weeks, the US is due to start taxing $US34 billion in Chinese goods. Beijing has vowed to retaliate with its own tariffs on US soybeans and other farm products in a direct shot at US President Donald Trump's supporters in America's heartland.
President Donald Trump on June 20. Source: AAP
The tit-for-tat conflict between the US and China - the world's two largest economies - is poised to escalate from there.
"We oppose the act of extreme pressure and blackmail by swinging the big stick of trade protectionism," a China's Commerce Ministry spokesman said Thursday.
"The US is abusing the tariff methods and starting trade wars all around the world."
Cecilia Malmstrom, the EU's trade commissioner, acknowledged that the EU had targeted some iconic American imports for tariffs, like Harley-Davidson motorcycles and bourbon, to pressure US leaders.
John Murphy, a senior vice president at the US Chamber of Commerce, estimates that $US75 billion in US products will be subject to new foreign tariffs by the end of the first week of July.
We've never seen anything like this Mary Lovely, Syracuse University
"We've never seen anything like this," said Mary Lovely, a Syracuse University economist who studies international trade - at least not since countries tried to wall themselves off from foreign competition during the Great Depression.
Mr Trump ran for the presidency on a vow to topple seven decades of American policy that had favoured ever-freer trade among nations. He charged that a succession of poorly negotiated accords - including the North American Free Trade Agreement and the pact that admitted China into the World Trade Organization - put American manufacturers at an unfair disadvantage and destroyed millions of US factory jobs.
He pledged to impose tariffs on imports from countries that Mr Trump said had exploited the US. Late last month, Mr Trump proceeded to infuriate US allies - from the EU to Canada and Mexico by imposing tariffs of 25 per cent on imported steel and 10 per cent on aluminium.
