The two lobes of the Human Sphere are more or less united in theory into a single Imperium Solum Sacrum, or Holy Solar Empire, but in practice the First Lord of the Terran Star League rules as Westerly Emperor of the Inner Sphere Sword Worlds, and the Padishah Hegemon of the Villein Star Hegemony rules as the Easterly Emperor of the Outer Sphere Novo Terran Star Hegemony.
Both the Star League and the Star Hegemony are successor states to the Old Hegemony which once ruled all the worlds of man for five long, life-span extended generations, before the civil wars and disasters of the Occultation of the Stars broke the Old Hegemony in the long emergency of the Interregnum.
The other major race of Man, the Villein, where once themselves ruled by the fungoid serpent-parasites called the Shan of Shaggai, who burrowed into the brain-stems of their subjects and posed as Gods who ruled their cattle-subjects absolutely and nourished themselves from the faith-food and blood-food of their subject-worshipers. This state of affairs lasted until the young men of the Ancient Earth Alliance, together with their green blooded Rhomulani allies, cast out the Shan, and ground their heads beneath the soles of their jack-boots. Officially the Shan are extinct, but rumors abound of prideful men willing to strike terrible bargains for unholy powers and long life.