Sweeping tariffs on imports from Canada, Mexico and China went into effect just after midnight on Tuesday, raising U.S. tariffs to levels not seen in decades and rattling foreign governments and businesses that depend on international trade.

As of 12:01 a.m. Tuesday, the Trump administration added a 25 percent tariff on all imports from Canada and Mexico. The administration also added another 10 percent tariff on all imports from China. That comes on top of a 10 percent tariff on Chinese goods put into effect just one month ago and a variety of older levies, including those that remain from the China trade war in Mr. Trump’s first term.

The tariffs will make good on President Trump’s campaign promise to rework America’s trade relations, and they are likely to encourage some manufacturers who want to sell to American customers to set up factories in the United States, instead of other countries.

But by altering the terms of trade between the United States and its largest economic partners, the tariffs will also probably rattle supply chains, strain some of the country’s most important diplomatic relationships and add significant costs for American consumers and manufacturers.

Canada, Mexico and China are the three largest trading partners of the United States, accounting for more than 40 percent of both U.S. imports and exports last year. The three countries supply the bulk of crude oil, beer, copper wire, toilet paper, hot-rolled iron, cucumbers and chocolate imported by the United States, as well as a dizzying array of other products.

The tariffs came as somewhat of a surprise, given that Mexico and Canada have gone to great lengths in recent weeks to convince the president that they were stepping up enforcement of their borders. The president initially threatened in November to impose the tariffs, saying that the three countries were not doing enough to halt the flow of drugs and migrants into the United States.

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