 Complete the following phrase:  He initially studied philology at the University of Bonn, where one of his instructors was Friedrich Wilhelm Ritschl 1806-1876. Afterwards he studied history under Georg Waitz 1813-1886 at the University of Göttingen. In 1864 he earned his doctorate at the University of Berlin, and two years later obtained his habilitation. He later performed historical research in Siena and Rome. As a combatant during the Franco-Prussian War, he was killed in the 