Complex sentence: Due to a restructering of the German football league system however, the five "Regionalligas" where replaced by the two "2nd Bundesligas", no promotion from the third to the second tier was available that season.
Split into simpler sentences: Due to a restructering of the German football league system however, the five Regionalligas were replaced by the two 2. Bundesligas, no promotion from the third to the second tier was available that season.