Complex sentence: He returned to Herford, but in 1920 moved to Berlin, where he became manager of an airline, the Deutsche Luft Lloyd GmbH, which, however, failed in 1922--3.
Split into simpler sentences: He returned to Herford, but in 1920 moved to Berlin. Here he became manager of an airline, the Deutsche Luft Lloyd GmbH, which, however, failed in 1922--3.