His goal was simple. To deal with his competitors and gain territory.
Hell had a fairly simple division. Basically, one had to dominate areas where there were Reincarnation Wheels, something difficult that went beyond saying that a particular area was one's own. Achieving recognition of an area where there was one of these special phenomena went beyond beating the owner of the area.
But the more Reincarnation Wheels one had in their domain, the greater their benefits in the Hell and the greater their influence.
Above a certain value, one could even claim the position of a Devil and remove someone other than their own master from one of the Devil positions before attempting to conquer the Throne of Hell.