Original: Since the Duke of Saxony was considered one of the prince-electors electing a new Holy Roman Emperor, conflict arose between the lines of Lauenburg and Wittenberg over the issue of who should cast Saxony's vote.
Simplified: Since the Duke of Saxony was considered one of the prince-electors electing a new Holy Roman Emperor, there was an argument between the lines of Lauenburg and Wittenberg about who should cast Saxony's vote.