The Hegemony was established as part of the Bugger War to unify Earth against the new alien threat. The Hegemon is its most prominent political figure and is considered the ruler of the planet Earth.
Its realm and jurisdiction is the entire planet of Earth, leaving extraterrestrial policing to the International Fleet and extraterrestrial politics to the Starways Congress.
Prior to the Hegemon, the Second Warsaw Pact was a unification of eastern Europe and Asia. This entity still exists as a separate yet supplicant entity within the Hegemony.