A Kingdom is the highest type of governance in Crusader Kings. The ruler of a Kingdom has the corresponding King title, and gains prestige from the number of Dukes and King Titles he (or she) holds. Like any Duke title, a King does not need to own a single piece of land in the corresponding Kingdom, it can be inherited or taken by war without any corresponding county or duke titles taken as well. However, to get a claim on a King title is prohibitively expensive (15000 prestige on the highest difficulty), and it usually easier to work your way into an inheritance through marriage or by usurping the title than spending prestige to claim it.