Our structure is a failure. You saw how the Jeeno almost destroyed our world and have taken many of our planets, we must reorganize ourselfs into a better efficiant state.
—Daer'eyn'ath
The Dark Galactic Empire was an intergalactic government, which preceded the Sith Empire, and was formed to create a more secure and powerful government.
It was ruled by the Dark Emperor and the Sith-Imperial High Council. Many branchs of the government, such as the Imperial Senate and the Imperial Planetary Governors, remained the same from the last Empire. The Dark Galactic Empire became more equivalent with both Sith and Imperial having similar powers alike. Order in the Empire was upheld by the powerful soldiers, Dark Troopers, of the Dark Trooper Corps but not to the point of oppression.
Dark Sided Force users were welcomed into the Empire such as Dark Jedi, who were not allowed before, and other Dark Sided force groups were allowed but the Sith were always on the top amongst these groups. The Dark Galactic Empire was reorganized in a way to protect the Empire from internal conflicts and with the new allies the Empire received, the military force increased and would be able to protect from outside forces.
This new Empire was formed after the near destruction of Dol Glorath during the Force War when leaders realized their system was failing allowed the Jeeno to claim Dol Glorath.