What I find very interesting about the Battle of Leipzig a.k.a. Völkerschlacht bei Leipzig (Battle of Nations at Leipzig) between France and a coalition of Prussia, Russia, Austria and Sweden is that Jean Bernadotte, a former marshal under Napoleon, now fought on the side of the coalition with the Swedish forces that he lead himself. He was the newly elected heir presumptive of the sickly King of Sweden (Bernadotte, an early proponent of the French Revolution, allegedly had "mort aux rois!", literally "death to kings!" tattooed across his chest, which I find very ironic).
Another interesting event that occured during this battle was the defection of over 5000 Saxon and Württembergian troops that originally fought on the French side. Saxony and Württemberg both were part of the Confederation of the Rhine and became Kingdoms following the dissolution of the Holy Roman Empire in 1806. After the Battle of Leipzig, many member states of the Confederation of the Rhine joined the coalition against Napoleon until the Confederation was finally dissolved by the coalition in November 1813, making the member states independent.