These documents , signed when he was elected as a King of Poland , promised that the then - Swedish territory of Estonia would become part of the Commonwealth .
Sigismund began his plans in 1599 , when he confirmed the pacta conventa .
These documents , signed when Sigismund was elected as a King of Poland , promised that the then - Swedish territory of Estonia would become part of the Commonwealth .
Sigismund began his plans in 1599 , when he confirmed the pacta conventa .