Story highlights Mattis sends message of reassurance to South Korea and Japan

Questions raised over whether Mattis crafts America's Asia policy

(CNN) Huge sighs of relief must be emanating through the corridors of power in Japan and South Korea.

The two Asian countries were chosen as the destinations for the first overseas visit by a Trump Cabinet member and US Defense Secretary James Mattis gave Seoul and Tokyo exactly what they were looking for.

Both countries had been stunned by comments made by President Donald Trump on the campaign trail that suggested that they should develop their own nuclear weapons to defend themselves and pay more toward the cost of troops stationed in the region.

Mattis laid all those concerns to rest in his four-day visit, promising an "effective and overwhelming" response should provocative neighbor North Korea launch a nuclear attack and said US defense commitments in East Asia were "ironclad."

He even told his Japanese counterpart Tomomi Inada that her country had "been a model of cost sharing."