The Earth Empire is the oldest organisation in the Human race, and was formed sometime in the 3rd millenium and existed sometime until the mid-5th millenium, it's sole purpose was to dominate the colonies and destroy all that refuse it's control.
The Earth Empire was formed on Earth and had a government structure similar to the Russian Empire, with the leader of government known as the Csar and the government was a semi-democratic organisation which is run by not only the Csar but a parliment with ministers that represent the Earth's people. The Empire was presumably created sometime before or after 3095 as a way to govern Earth and all founded colonies. The Empire enjoyed considerable prosperity following colonisation of Alpha Centauri in 4175, but this was due to a ruthlessly authoritarian governing of the colonies, in order to send a majority of exports to Earth, as with the Csars' wishes. This evetually led to widespread rebellion known as the First Colony War.
The Earth Empire's colonial representative was the Colonial Navy with its vast battleships, fleets of fighters and millions, possibly billions of troops.