How do you become a duke?

There are three ways to become a duke. 1. You inherit the title from a male family member. 2. You perform a great service for a monarch. 3. In certain nations such as France, the land not the individual holds the title. Thus, if you purchased the estate of Sainte Camille, and a dukedom was linked to the land.. so long as you held the land you could style yourself " His Grace, The Duke of Sainte-Camille".