Demonstration of Power
While Silver was racking his brains about how to put Jin's plans into action, the massive 'big brain' System was simultaneously taking into account the possibility that the Southern Region could be turned into a prospective country under their rule. Since 'just a city' such as Pandapolis was not enough, the System wanted Jin to have a 'mock country' to rule.
However, Jin did not care about all these plans for the future. His priorities were to ensure proper housing, sanitation and an overall better quality of life for the Southerners which he now felt responsible for.
All those ancient feuds stemmed from humans and monsters fighting for the survival of their population. As long as the humans could be fed and sheltered properly, he believed that cooperation with their former enemies might be possible… at least in theory. He was not naive enough to believe that everlasting peace could ever be realized so easily, otherwise others would have done so already.