In his remarks Monday, Mattis made clear that the USA and Japan are prepared for future missile threats.
Trump, who has been a vocal critic of the United Nations in general, heads to his first UN General Assembly in NY this week, where he will meet with world leaders and also address North Korea threats. Whatever else anyone says, the core issue in this year's General Assembly will be the North Korean nuclear problem.
During the mission, USA and ROKAF aircraft flew across the Korean Peninsula and practiced their attack capabilities by releasing live weapons at the Pilsung Range training area.
The North also fired a ballistic missile over Japan and into the Pacific on Friday, responding to fresh new United Nations sanctions with what appeared to be its longest-ever missile flight.
On Sept. 3, North Korea conducted an underground nuclear test that was by far its most powerful to date. It is likely that President Moon is also deeply concerned about what his speech should cover.
Mattis also confirmed that the United States and Seoul had discussed the option of sending limited-size "tactical" nuclear weapons to South Korea. It's true that in a sensitive situation where North Korea is launching ballistic missiles despite United Nations resolutions, South Korea's range of options is considerably narrow.
Trump and South Korean President Moon Jae-In spoke by phone Saturday night and pledged "stronger pressure" on Kim Jong-Un's regime, the South's presidential office said, adding that the North must be made to realize that "further provocation" would put it on a "path of collapse". But he also needs to clearly convey to world leaders that sanctions must only serve as a lead in opening the door to dialogue.
He said that Washington's strategy has been to undertake a peaceful pressure campaign premised on "four nos" meant to reassure Pyongyang: not seeking regime change, a regime collapse, accelerated reunification of the Korean Peninsula, or a reason to send US forces north of the demilitarized zone. He is jeopardizing global security and trying to start a war with North Korea.
China and Russian Federation have repeatedly called for a peaceful solution to the crisis. In their latest call, the White House said Trump and Moon had committed to "take steps to strengthen deterrence and defense capabilities" of South Korea, offering no details of how it might do so. But the unilateral foreign policy that Trump aspires to differs in many ways from the desire for peace and coexistence found in other countries.