President Trump’s announcement of sweeping tariffs on America’s trading partners has widened the rift between the United States and some of its closest allies while reconfiguring the global economic order.

Mr. Trump’s plan, which he unveiled on Wednesday and is calling “reciprocal,” would impose a wave of tariffs on dozens of countries. Among America’s most important trading partners affected were the European Union, which will face 20 percent tariffs under the plan, and China, which will absorb an additional 34 percent on top of existing levies.

The new tariffs represent “a major blow to the world economy,” Ursula von der Leyen, the president of the European Commission, said in a press statement early on Thursday morning. “The global economy will massively suffer. Uncertainty will spiral, and trigger the rise of further protectionism.”

Mexico and Canada, who have especially close economic relationships with the United States, would not be subject to any new tariffs beyond the levies the president had previously announced, on imported vehicles, vehicle parts, steel, aluminum and any other goods not traded under the rules of the U.S.-Mexico-Canada Agreement.