Defense Secretary Jim Mattis is making his second trip this year to Vietnam, and it's a sign of how much the Trump administration is trying to counter China's military assertiveness by cozying up to smaller nations in the region.

The visit begins Tuesday and shows how far U.S.-Vietnamese relations have advanced since the Vietnam War.

Mattis will visit Ho Chi Minh City, the most populous city and the economic center. It used to be known as Saigon.

Mattis also plans to visit an air base and meet with his Vietnamese counterpart.

The trip originally was to include a visit to Beijing, but that stop was canceled amid rising tensions over trade and defense issues.

These tensions have served to accentuate the potential for a stronger U.S. partnership with Vietnam.