US Secretary of Defense James Mattis’ visit to Korea on Thursday is expected to open the door to a new diplomatic environment for South Korea.

His visit is the first overseas trip by a member of the US cabinet since Donald Trump took office as president. Korea is his first country to visit. It reflects how serious and urgent the North Korean nuclear issue is to the Trump government.

North Korea has been heightening tension on the Korean Peninsula. Recently its nuclear reactor at Yongbyon showed a water plume, indicating that it has resumed operation of the facility capable of producing plutonium used to make atomic bombs. A North Korean diplomat repeated the Pyongyang regime’s threat to be able to test-fire an intercontinental ballistic missile at any time, at any place. North Korean TV networks repeatedly broadcast footage of past missile launches. Its leader, Kim Jong-un, frequently inspected military units.

The international community has slapped a series of sanctions on North Korea for its nuclear and missile tests. Its ally, China, joined the international community, but the Trump government wants China to put more pressure on Pyongyang, saying Beijing wasn’t doing enough to help the US rein in North Korea.

The US has cranked up its diplomacy on North Korea with Mattis’ visit to Seoul. He is scheduled to hold talks with Minister of National Defense Han Min-koo on Thursday and then leave for Japan the following day.

Diplomatic activities over the North Korean program to develop nuclear weapons have taken place with the US and South Korea on one side and China and North Korea on the other.

Now a new diplomatic stage has been set with the inauguration of a new US government that takes a hard line on North Korea. They should take lead roles in resolving the North Korean nuclear problem.

The South Korean government, for one, should keep up its own diplomatic efforts to bring the international community together against North Korean nuclear arms.

Seoul and Washington should take the initiative on the diplomatic landscape because North Korean nuclear arms are an issue directly linked to the survival of the Korean people. Atomic bombs, which can kill millions of people at once, must not be used on the peninsula.

If China takes the initiative, the issue of North Korean nuclear weapons is likely to be left unresolved. China is North Korea’s protector, chief trading partner and economic lifeline. Some analysts say China’s first priority is to maintain stability on their border, which means they are unwilling to put North Korea’s survival at risk, because it views North Korea as a buffer between its border and South Korea.

If China takes diplomatic leadership over the North Korean nuclear issue, it will likely press South Korea harder to revoke its decision to deploy the Terminal High Altitude Area Defense battery, an advanced US missile defense system. It will also likely try to pull South Korea apart from the US and bring it into the Chinese side. South Korea will face a more complex diplomatic environment and a longer way to go to the resolution of the North Korean nuclear problem.

One may argue that South Korea can avoid Chinese retaliation over THAAD if it does as China tells. Of course, retaliation may be lifted but it will come at a higher price than damage from retaliation. South Korea will be blamed by its Korean War allies for changing its ground. The Americans may clamor for the withdrawal of US troops. South Korea risks falling into a more dangerous state of national security if its alliance with the US is broken.

Undeniably, Chinese retaliation over THAAD hurts the South Korean economy. Seoul needs to get its difficult position across to the US and ask it to deal with Beijing’s anxiety over the system. China should stop harassing its smaller neighbor over the US antimissile system and talk with the US directly.

Korea could advance its interests through brisk diplomacy. It has to keep warning the international community of the North Korean nuclear threat and ensure Pyongyang knows that the world is united against its nuclear arms ambitions.

Opinions differ as to how long the US government’s hard-line stance will last. But a war of nerves between the US and China for diplomatic initiative over North Korea is expected to continue in the early days of the Trump administration, and the two giants may find common ground at some point.South Korea is on the threshold of a different diplomatic landscape. It should set off on the right foot.