President Donald Trump would have unique influence over the operations of U.S. Steel under the terms of the investment being made by Nippon Steel.

Nippon Steel Corp. won conditional U.S. approval for its $14.1 billion purchase of United States Steel Corp., capping a lengthy saga in a tie-up that will create one of the world’s largest steel companies.

The companies said they had entered into an agreement with the U.S. government to alleviate any national security concerns.

For Japan and many other countries, the vulnerability that comes with relying on U.S. markets has become startlingly clear. First came tariffs on Canada, China, and Mexico. Then, in February, the administration introduced a 25 percent tariff on steel and aluminum (this week,