Complex sentence: Then, Martenstein took up for a short time the line of the culture editorship at the "Abendzeitung (AZ)" in Munich, however he returned a little later to leading editor of the daily mirror.
Split into simpler sentences: Then, Martenstein took up for a short time the line of the culture editorship at the "Abendzeitung (AZ)" in Munich. However, he returned a little later to leading editor of the daily mirror.