Complex sentence: Prussia's reward for its part in France's defeat came at the Congress of Vienna, where Prussia was granted most of its lost territories and considerably more, including 40% of the Kingdom of Saxony and much of Westphalia and the Rhineland.
Split into simpler sentences: Prussia's reward for its part in France's defeat came at the Congress of Vienna. It regained most of its pre- 1806 territory and considerably more, including 40% of the Kingdom of Saxony and much of Westphalia and the Rhineland.