Four North Korean soldiers and four South Korean soldiers stand guard April 26 at the border village of Panmunjom in the demilitarized zone. North Korean leader Kim Jong Un and South Korean President Moon Jae-in will plant a commemorative tree and inspect an honor guard together after Kim walks across the border April 27 for their summit, Seoul officials said. (Hwang Kwang-mo/Yonhap/AP)

When the inter-Korean summit takes place Friday, it will be the first high-level talks between North and South in more than a decade. Seoul and Pyongyang have had just four important high-level meetings in the past 40 years, in fact.

How do the high-level talks in 1972 and 1991 and two inter-Korean summits in 2000 and 2007 play into Friday’s summit? And what are the domestic political and legal considerations on South Korean President Moon Jae-in’s road map for reunification and peaceful coexistence?

The joint statement of 1972

The high-level talks of 1972 adopted a joint statement aimed at improving inter-Korean relations. The notable outcome was the two sides’ agreement on three principles for reunification: independence, peaceful means and grand national unity. In other words, reunification on the Korean Peninsula had to be achieved peacefully and without any external influence, and transcend the two different ideologies and systems.

The 1991 Inter-Korean Basic Agreement

In 1991, Seoul and Pyongyang signed the Inter-Korean Basic Agreement, which included specific measures to enhance inter-Korean relations in both military and nonmilitary areas. What distinguished the 1991 meeting from the 1972 one is an unspoken modification in the principle of grand national unity.

Two Koreas had independently developed their political systems for decades, leaving a gap in their ideologies that was too deep to bridge. For this reason, a period of peaceful coexistence was deemed necessary to shorten the gap for eventual unity. In 1991, Seoul and Pyongyang promised to respect and recognize each other’s systems and not to interfere in the other country’s internal affairs. This means that achieving “grand national unity” through reunification was delayed for practical reasons.

The 2000 summit

The 2000 summit established more substantive formulas for peaceful coexistence as an interim step before reunification. Seoul and Pyongyang proposed a confederation system and loose federation system, respectively. Under Seoul’s proposal, there would be one nation, two states and two governments. North Korea saw a loose federation composed of one nation, one state and two regional governments.

The primary difference was how much sovereignty each side might be willing to cede to a central body. South Korea preferred to treat a central body as a matter of formality for phased reunification so that two Koreas could coexist as completely independent states. Conversely, North Korea insisted that a central body represent a Korean federation as one state in the international community while the two governments maintain autonomy — like the China/Hong Kong model.

The 2007 summit

Like the 1991 agreement, the joint declaration adopted at the 2007 summit included specific improvements to inter-Korean relations in both the military and nonmilitary realms. The two sides also reconfirmed the reunification goals set in 2000 and agreed to adjust the domestic legal and institutional framework to gear their relations toward reunification.

What was new in 2007 were discussions about nuclear issues and the peace regime, in the context of regional matters. The two sides agreed to establish a permanent peace regime. From the North Korean viewpoint, ending the Korean War requires a peace treaty between the United States and North Korea. Presumably for this reason, Seoul and Pyongyang agreed to promote talks among the three or four parties directly related to ending the Korean War, implying two Koreas and the United States, with a possible extension to China.

At that time, there had been Six-Party Talks since 2003 to resolve North Korean nuclear issues. During the 2007 summit, South and North promised to cooperate to implement the Six-Party agreements to resolve “nuclear problems on the Korean Peninsula.” This suggests that the two leaders at the time perceived the peace regime and denuclearization issues as a broader regional matter, beyond simply inter-Korean affairs.

And now for 2018?

It’s safe to assume that the 2018 inter-Korean summit will also look to build upon the steps taken at the previous four talks. South and North would reconfirm their will to achieve denuclearization on the Korean Peninsula. Since President Moon Jae-in also views the peace regime and denuclearization as regional matters, Moon will no doubt look to promote a summit between President Trump and Kim Jong Un for more substantive discussions on denuclearization and a peace treaty between them.

In the realm of inter-Korean affairs, the two sides may try to tackle some specific issues this week. For example, the talks could echo the steps taken in 2007 to promote military and nonmilitary cooperation — including mechanisms to reduce the military tension near the DMZ and promotion of cultural exchanges. Given the sanctions on North Korea, discussion on economic cooperation could be limited this time around.

What might “peaceful coexistence” look like?

As his long-term goal, Moon has already expressed his will to see the Korean Peninsula as either a loose federation or confederation since he does not think there is a difference between the two systems. But there are a few political and legal constraints on his vision.

According to the opposition Liberty Korea Party, the idea of a Korea federation would eventually entail the end of the U.S.-South Korean alliance. Here’s why — within one state, it would be difficult to have one regional government maintain a protective alliance against the other. Any aggression between the two would likely be treated as a civil war — this would make other states reluctant to intervene, which was the Soviet Union’s argument during the Korean War.

But South Koreans may not be fully ready to accept a Korean federation. A 2005 poll revealed that 65 percent of South Koreans preferred reunification by absorbing North Korea. Only about 28 percent supported the idea of a Korean federation.

In 2012, a poll found that 78 percent of South Koreans believed that the U.S. presence in their territory was necessary; 48 percent thought U.S. troops should remain post-reunification, while 45 percent disagreed.

There’s also a legal hurdle. The South Korean constitution defines the territory of South Korea as the whole Korean Peninsula and requires that reunification be based on liberal democracy. This means that recognition of North Korea as a legitimate state on the Korean Peninsula clashes with South Korea’s understanding of its territory and its principle of liberal democracy. What’s the bottom line? Achieving peaceful coexistence may require Moon to amend the constitution.

Assuming the talks go well, there will be a lot of follow-up activity after Friday’s summit. Moon would make his best efforts to realize his intermediate goals — denuclearization and a peace regime on the Korean Peninsula — through the U.S.-North Korea summit.

For inter-Korean affairs, Moon’s next step would be to institutionalize cooperation between the two Koreas. The biggest challenges at home will be relieving domestic concerns — and handling legal constraints on his long-term vision for peaceful coexistence.

Hyuk Kim is a nonresident research fellow at the Pacific Forum Center for Strategic and International Studies.