Leaders of South Korea, the United States and Japan opened a new era in their partnership through their landmark summit last week.

They will hold trilateral summits and meetings between foreign ministers, defense ministers, national security advisers at least annually and also launch annual meetings of commerce and industry ministers.

They formed a quasi-alliance in which they agreed to consult one another and act as one in the fields of diplomacy, security, economy and technology.

Diplomacy and security experts evaluate the outcomes from the summit as the biggest change since the Korea-US alliance was born in 1953.

The summit is also significant in that it formed an economic and security bloc of three countries which account together for 32 percent of the global gross domestic product and whose leaders meet each year to discuss a wide range of issues.

Above all, it elevated the trilateral security cooperation to a new level.

North Korea keeps escalating its nuclear and missile threats, and its solidarity with China and Russia are getting closer. On the occasion of the 70th anniversary of the Korean War armistice agreement last month, Chinese President Xi Jinping sent a personal letter emphasizing comradeship to North Korean leader Kim Jong-un, while Russian President Vladimir Putin sent his Defense Minister Sergei Shoigu to Pyongyang.

As North Korea, China and Russia are cementing their unity, it has become urgent for South Korea, the US and Japan to tighten their security cooperation.

Meanwhile, obviously there were limits on trilateral cooperation among South Korea, the US and Japan largely due to conflicts over history and other issues between Seoul and Tokyo. South Korea, the US and Japan are connected through Korea-US and US-Japan alliances, but South Korea-Japan ties, one side of a triangle, was not so stable.

South Korea, the US and Japan held summits but all of them on the sidelines of multilateral meetings. It was the first time their leaders met for a standalone meeting. Such summit itself is meaningful. It is also noteworthy that US President Joe Biden invited South Korean President Yoon Suk Yeol and Japanese Prime Minister Fumio Kishida to the Camp David presidential retreat in Maryland, a famous venue where historic deals were reached.

The three leaders spent their longest-ever time together and agreed to set up a comprehensive and multilayered cooperation channel. They showed a will to surpass existing limitations on trilateral security cooperation.

The greatest accomplishment of the summit, perhaps, was the decision to institutionalize the partnership in the form of documents. In the past, the US-Korea and US-Japan alliances have worked individually with the US playing a pivot, but the three leaders put trilateral cooperation on a more sustainable footing. It was, in effect, a step that precedes the formation of an alliance.

In particular, the agreement to hold summits at least once a year is expected to make it hard to reverse the progress of partnership. Even if Seoul-Tokyo ties turned sour temporarily or even if a US-centered candidate becomes president, it would be difficult to avoid an institutionalized summit with allies.

If Seoul, Washington and Tokyo want to maintain the trilateral cooperation stably, it is important to prevent historical tension and other issues involving South Korea and Japan from running it aground. If Seoul-Tokyo relations deteriorate again, the outcomes from the latest trilateral summit will all disappear. In this respect, South Korea-Japan relations are important, and Tokyo needs to respond more sincerely to Seoul's moves to improve bilateral relations.

Cooperation among South Korea, the US and Japan stands opposite to solidarity among North Korea, China and Russia. Confrontation between the two fronts will likely become clearer. North Korea's provocations will likely get bolder. The government in Seoul needs to draw up plans to reduce resistance from China, which is a major trading partner for South Korea. It must formulate new response strategies based on the position that the window to dialogue is always open if Pyongyang is sincere and that Seoul can cooperate with Beijing for mutual common interests.