Complex sentence: While electing an emperor, who was also the ruler of a foreign power, had not happened since the ruler of Sicily, Frederick II, was elected in 1211, France and the Empire had not been joined since the days of the Carolingian dynasty.
Split into simpler sentences: While electing an emperor, who was also the ruler of a foreign power, had not happened since the ruler of Sicily, Frederick II, was elected in 1211. On the other hand, France and the Empire had not been joined since the days of the Carolingian dynasty.