Complex sentence: In the French Sixth Army sector, one railway line from Amiens led to Bray on the north bank but on the south bank there were no rail lines, so road-trains carried supplies from Amiens to Foucaucourt.
Split into simpler sentences: In the French Sixth Army sector, one railway line from Amiens led to Bray on the north bank but on the south bank there were no rail lines. In order to supply the south bank, road-trains carried supplies from Amiens to Foucaucourt.