Hi. In order to become a European boss, all countries from the first stage to the last must be finalized and must we win a cup or can we start the championship at any stage without winning a cup?
To gain the European Boss Achievement, you only need to achieve your goal/objective in all the European countries/Leagues. The cup does not count for this achievement.
And yes, you can start at any stage of the league so long as you can join the league.