From Leveling Up the Hero to Leveling Up a Nation

It feels like I (27 y/o) who specialized in [Training] skill was no longer necessary for the Hero's party which had grown stronger to a certain degree. At first, I was the center of the party but in the end, the hero dismissed me from the party. However, because I had "Made a great contribution to the party until now," I received a small Fief instead of retirement money. With my heart feeling the loneliness of leaving the adventures frontline and after seeing the seven villages with their 2500 population of my territory, I had the following thought, "I wonder if I train these people, won't my territory become strong enough that could even defeat the demon lord?"