Frederick I decisively secured his family's possessions with the implementation of the primogeniture in 1685. His son and successor Duke Frederick II gained further Ernestine territories upon the death of Duke Albert V of Saxe-Coburg in 1699 and Duke Christian of Saxe-Eisenberg in 1707.
Frederick I solidified his family's possessions through primogeniture in 1685. His son, Duke Frederick II, gained additional Ernestine territories upon the deaths of Duke Albert V of Saxe-Coburg and Duke Christian of Saxe-Eisenberg in 1699 and 1707 respectively.