Complex sentence: Upon Rudolf's death, Emperor Matthias confirmed Saxony's rights to the fief, rekindling the dispute and the conversions of Ernst and Wolfgang Wilhelm to Calvinism and Catholicism respectively completely restructured their past alliances.
Split into simpler sentences: Upon Rudolf's death, Emperor Matthias confirmed Saxony's rights to the fief, rekindling the dispute. Furthermore, the conversions of Ernst and Wolfgang Wilhelm to Calvinism and Catholicism respectively completely restructuring their past alliances.