Complex sentence: John Frederick (25 April 1625 in Herzberg am Harz--18 December 1679 in Augsburg) was duke of Brunswick-Lüneburg and ruled over the Principality of Calenberg, a subdivision of the duchy, from 1665 until his death.
Split into simpler sentences: John Frederick (25 April 1625 in Herzberg am Harz--18 December 1679 in Augsburg) was duke of Brunswick-Lüneburg. He ruled over the Principality of Calenberg, a subdivision of the duchy, from 1665 until his death.