The election of the leader of the Democratic Party, namely the Minjoo Party, puts an end to the multi-annual centre-right political hegemony represented by the old Saenuri Party, which last February, following the impeachment and dismissal of former President Geun-Hye Park, split off and changed its name to Liberty Korea Party.
The turnout rate was particularly high, with 77.2% of people who cast their vote.
However, who is the 66-year-old lawyer who has a long history as human right lawyer and civil rights defender?
He has already had significant political experience as Chief of Cabinet of former South Korean President Roh Moo-Hyun. He was also a member of the South Korea’s Parliamentary Assembly and finally founded the progressive daily newspaper Hankyoreh.
At political level, the new South Korean President wants, above all, peaceful reunification with North Korea.
He is reproposing the Sunshine Policy adopted by two former South Korean President, namely Kim Dae-Jung and Roh-Moo Yun, who still seems to be the reference point for Moon Jae-In.
Moreover, the newly-elected President has also declared he is a "friend of America", especially because it spared South Korea from the experience of war Communism and because it long sustained its economic growth.
In essence, the new South Korean leader wants a rebalancing of relations between South Korea and the United States and, in particular, South Korea's full autonomy with regard to the reunification policy with North Korea.
Obviously, the very idea of reunification between the two Koreas is based on autonomous enhancement and upgrading of South Korea’s military system and on a project for economic merger between the two old regions - a tragic relic and memory of Cold War in Asia, the region in which there was the fiercest and longest clash between the United States, the USSR and China.
As Park Geun-Hye said in 2014, reunification would be an "economic bonanza".
That idea was supported both by Barack Obama and Xi Jinping, who were both interested in defusing the regiona militarily and, above all, in creating an economic and financial success case in the Pacific, so as to support both China’s growth and Japan's economic cycle.
The only one that explicitly opposed said idea in 2014 was Rodong Sinmun, the official newspaper of the Central Committee of the North Korean Workers’ Party.
The issue, however, is complex, considering that North Korea's nuclear and missile activities have led to a long sequence of UN Security Council’s Resolutions, ranging from No. 1718 to 1874 and 2087, as well as a set of harsh economic sanctions.
North Korea needs to give priority to its nuclear and military potential compared to the reunification project, as it is the only guarantee for the stability of its ruling class.
Conversely, South Korea needs to internationalize the Korean issue, so as to permit a reunification which, in its plans, would enable North Korea to redress its economy and create a productive boom that would make the reunited Korea a big and stable "Asian tiger".
South Korea thinks of reunification mainly as an extraordinary opportunity for its economic growth.
Moreover, this would also be in US interest.
Obviously, North Korea's progressive destabilization would endanger China, which has 1,420 kilometres of terrestrial borders with North Korea, as well as the Russian Federation, which has 17 kilometres of terrestrial borders with North Korea and 22.1 kilometres (equivalent to 12 nautical miles) of maritime borders.
If the polarity between China and the United States loosened, exactly in relation to the future of North Korea, this would be the primary strategic key to reunification between South and North Korea.
Russia would be the natural reference point for restructuring the North Korean nuclear and missile potential, which would become a guarantee for security throughout the South Pacific region.
On the economic front, South Korea’s new President is well-known for his fight against the chaebol, namely the large industrial conglomerates which have so far produced both South Korea’s economic growth and the many corporate restrictions and impediments that prevent it today.
Furthermore, South Korea records a very low birth rate, which naturally weakens its economic momentum, and a welfare crisis that, for the first time since the 1950s, makes the ghost of mass poverty loom large.
Hence currently the political and economic dialectics in South Korea lies between the "protected" and the "marginalized", in a two-thirds society where poor people increase and the protection for those who are still at work decreases, matched by a parallel increase of the unemployed, the old "reserve production army" stabilizing wages at their lowest level.
As stated by the new President, on the geopolitical front, South Korea shall "learn to say no to America", especially with regard to the THAAD missile defence network, which, however, should be largely paid by South Korea.
In addition, South Korea should "take the lead in the flow of events" regarding the nuclear threat posed by North Korea.
Translated into current language, South Korea could start a series of talks with North Korea so as to make it lower the military guard and, above all, put its defence directly into the hands of the national government - and not only of the relationship between South Korea and the United States.
Would it be enough? Yes, if the rejection of the THAAD system is followed by a series of economic and military measures to reassure North Korea.
Said measures would make the Russian Federation and China enter the Korean strategic framework and both countries are expected to rebalance the system, while the United States loosens its grip on South Korea.
From an economic viewpoint, the reunification of the two Koreas is supposed to cost a sum ranging between 25 billion and 3.5 trillion US dollars. The target should be the possible doubling of North Korea’s GDP four years after reunification.
And again, bearing these calculations in mind, reunification should cost additional 50 or 67 billion US dollars.
Hence, South Korea cannot bear these costs on its own and should raise at least 50% of the funds needed abroad.
Another scenario to be considered is the one which seems to be the most likely today, that is North Korea accepting the minimum number of domestic economic reforms needed to preserve the status quo indefinitely.
The second scenario - again for North Korea - suggests a short-term economic collapse that would entail huge costs both at humanitarian level and for securing North Korea’s nuclear, biological and conventional weapons, with a possible mounting of tensions in South Korea, which could not solve North Korea's implosion on its own.
A further possible scenario is a war between the two Koreas, which would trigger off unimaginable tensions in China, Russia, and Japan.
Obviously, at least since the 1990s, South Korea’s ruling class has assumed the primary criterion that - even avoiding the most dangerous and unfortunate choices - reunification will be a very slow process, in which no South Korean government will do anything to favour an economic, strategic or political crisis in North Korea.
Furthermore, 67% of people in South Korea believes that the two Koreas should be reunited, but 56% of South Koreans think that their country would lose, rather than benefit from the reunification process.
At geopolitical level, reunification could entail the strategic autonomy of Korea, with the North Korean armed forces leaving South Korea, thus eventually playing China against the United States and the other way round.
North Korea, however, is a buffer zone China needs to avoid an even closer alliance between South Korea and the United States.
China does not want reunification through the North-South war - the worst scenario for China - while the best scenario for it is the current status quo between the two Koreas preventing the humanitarian crisis in North Korea, which would spread to the Chinese territory, while South Korea keeps on recording high investment flows to China.
Hence, China backs North Korea, but only to a certain extent and it accepts the cost for maintaining the two Koreas, instead of envisaging reunification which would be China’s worst economic and security scenario.
In all likelihood, a reunited Korea would be a new Vietnam for China, as well as a non-compliant power and a strong economic competitor.
In the future, we can even imagine a maritime block between the United States and Japan, which would rebalance a continental block between China, Russia and the reunited Korea, while the United States should anyway succeed in persuading South Korea to avoid the military alliance with China.
Even from this viewpoint, in the future, the United States will tend to record a sequence of crises in the Korean region, both working on the assumption of a slow reunification, which would in any case make its armed forces leave the Korean peninsula, and working on the assumption that the status quo is maintained between the two Koreas, which is the situation in which the alliance between South Korea and China is optimal, thus also ensuring a faster and more stable reunification.
Obviously, the stability of the Korean Peninsula is essential also for Japan's security.
For Japan, the best scenario would be a status quo between the two Koreas leading to North Korea’s gradual denuclearization.
As a second option, Japan prefers Korea - also reunited - to remain friendly to the United States and, of course, to Japan, as well as economically open and enabling the US forces to keep on staying in the region.
South Korea wants to get closer to China as much as Japan shall get closer to the United States so as to preserve the balance of strategic potentials in the Korean Peninsula and in the rest of the old "co-prosperity area" of the Japanese Empire.
For Russia, the option is primarily economic: between 2000 and 2004 bilateral trade between Russia and North Korea grew by 36% and that between Russia and South Korea by 23%.
As to the two Koreas’ issue, the Russian Federation would like to reach a highly unlikely result: a united Korea in which Russia can make the South relinquish its security relationship with the United States.
More rationally, Russia wants a reunification maintaining the United States in the region and paradoxically keeping China away from it.
Nevertheless, in all likelihood, a reunited Korea would still be a primary asset for China, but only the US economy - together with the other major ones - could bear the cost of reunification, albeit slow.