There are two reasons they want both the expansion of manpower of the gang and the expansion of the territory that the gang controls.
The expansion of manpower is for them to find more good slaves. With more slaves, their power will increase and so will their safety.
As for the expansion of territory, it's just an excuse for them to kill a lot of people without doing it themselves.
This is the advancement requirement of the pathway of killing. They need to do a lot of indirect damage to people in order to become rank 5 killers.
While their slaves got busy, they got busy training and drinking energy water. The energy water was to provide spiritual energy for training and to also increase their spiritual power to 160 units, which is the peak of rank 4.
