TOKYO—As U.S. President Donald Trump threatens to overturn ties with America’s global allies, his defense minister gave an assurance to two Asian countries that depend on U.S. military support: we won’t abandon you.

U.S. Defense Secretary Jim Mattis pledged to uphold a commitment to defend Japan in a meeting with Japanese Prime Minister Shinzo Abe on Friday, after giving a similar guarantee to South Korea’s leadership.

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