Complex sentence: The Turco-German mission had left Kabul in 1916, however, by that time it had successfully convinced Habibullah that Afghanistan was an independent nation and that it should be beholden to no one.
Split into simpler sentences: The Turco-German mission had left Kabul in 1916. By that time, however, it had successfully convinced Habibullah that Afghanistan was an independent nation and that it should be beholden to no one.