Complex sentence: The First World War was the reason to build these railway links through inhospitable land but the main use was soon the peaking transport demand triggered by the diamond rush that developed after a railway worker picked up a diamond near Grasplatz station, 24 kilometers east of Lüderitz.
Split into simpler sentences: The First World War was the reason to build these railway links through inhospitable land. Soon however, transport demand peaked due to the diamond rush that developed after a railway worker picked up a diamond near Grasplatz station, 24 kilometers east of Lüderitz.