The root of the problem for Trump with Canada and Mexico stems from the North American Free Trade Agreement (Nafta), signed in 1994, which the president has called a "disaster" and "one of the worst deals anybody in history has ever entered into".
So let's mark the start of the conflict with a collection of some of the most illuminating quotes from the Chinese and American camps-bear in mind that the Chinese administration's views are generally expressed through state media-and from observers of the spat, who are anxious about where this will go.
But the tit-for-tat measures have escalated the trade dispute between the world's two largest economies and the world's commodities markets are increasingly embroiled in the bust-up.
Iowa State University economists calculated that from early March, when rumors of China's initial retaliatory tariff were circulating, through May producers lost $18 per hog, or more than $2 billion on an annualized basis.
Chinese media has promoted the message that the European Union is on China's side, officials said, putting the bloc in a delicate position.
Tariffs on USA pork to China could bring losses of more than $9 per head on all hogs slaughtered in the U.S. Beijing's retaliation will follow promptly.
Obviously the U.S. and China's economies are most at risk, although they're not the only ones.
USA crude oil prices reversed an early slide.
China sources a lot of components that go into its finished goods from these other countries.
Minutes after the United States put its long-threatened duties into effect just after midnight on Friday morning, a spokesperson for China's ministry of commerce said it would be matching them dollar-for-dollar.
It discussed economic threats and external risks, according to a government statement which added the country has "favourable conditions to win big risk control battles and cope with external risks".
Trump's tariffs on the EU, Canada and Mexico are for as much as 25% on imports of steel and aluminium, which the United States has imposed on grounds of national security. The head of the European Commission, Jean-Claude Juncker, said Mr Trump's fixation on a USA trade deficit in goods ignores a services surplus.
Still, China's stance is striking given Washington's deep economic and security ties with European nations.
United States tariffs on $34bn (£25.7bn) of Chinese goods have come into effect, signalling the start of a trade war between the world's two largest economies.
A foreign ministry spokesman, Hu Chunhua, on Friday gave no details of the increase.
Critics have long asserted that China runs roughshod over intellectual property rights. If Trump were to realise his ambitions there would be more domestic plants producing goods that China or Europe used to provide, and more jobs created in those plants.
China's government also announced it was adding this round of USA tariffs to an existing complaint filed with the WTO in April shortly after Washington unveiled the threat to punish Beijing for its policies on intellectual property. "We need these trade disputes to end".
But a manufacturing survey from the Institute for Supply Management shows they are not alone, while other companies say uncertainty is delaying investment plans. Chinese officials reject accusations of theft and say no foreign company is obligated to share technology. But EU officials expect any moves to be more symbolic than substantive.
"There is no way to meaningfully influence Chinese behavior on intellectual property without coordination among like-minded advanced nations, and presently there is nearly none", said Daniel Rosen of the economic research firm Rhodium Group.