Complex sentence: It was the only area of the partitioned Kingdom of Yugoslavia in which the German occupants established a military government, to exploit the key rail and riverine transport routes that passed through it, and its valuable resources, particularly non-ferrous metals.
Split into simpler sentences: It was the only area of the partitioned Kingdom of Yugoslavia in which the German occupants established a military government. This was due to the key rail and riverine transport routes that passed through it, and its valuable resources, particularly non-ferrous metals.