Complex sentence: She belonged to the Bernadotte dynasty, which had ruled in Sweden since 1818, when the founder, Jean-Baptiste Bernadotte, one of Napoleon's generals, was elected King of Sweden with the name of Charles XIV of Sweden.
Split into simpler sentences: She belonged to the Bernadotte dynasty, which ruled in Sweden since 1818. The founder was Jean-Baptiste Bernadotte, who had been one of Napoleon's generals, and who was elected King of Sweden with the name of Charles XIV of Sweden.