He was appointed professor at the University of Freiburg in 1863; in 1866, at the beginning of the Austro-Prussian War, his sympathies with the Kingdom of Prussia were so strong that he went to Berlin, became a Prussian subject, and was appointed editor of the "Preussische Jahrbücher". His violent article, in which he demanded the annexation of the Kingdoms of Hanover and Saxony, and attacked with great invective the Saxon royal house, caused an estrangement from his father, a personal friend of the king. It was only equalled in its ill humour by his attacks on Bavaria during 1870. After possessing appointments at the University of Kiel and the University of Heidelberg, he was made professor at Friedrich Wilhelm University (what is now named Humboldt University) in Berlin in 1874.