The Espheni Empire is an interstellar empire set up by the Espheni.
The Espheni were originally from another galaxy. However, a hostile force drove them from that galaxy into the Milky Way. The actions of this hostile force is the reason for the Espheni conquering planets and enslaving their inhabitants.(The Eye) Its later revealed that this force, the Dornia, was conquered by the Espheni over a thousand years ago and turned into the first Skitters. The survivors of the race are after them for revenge for their near-extinction.(Reunion) The Espheni were in fact taking over planets before this as the Espheni Queen mentions their prophecy of conquering the universe and how they tried to take over Earth 1,500 years before the present. However, the Espheni had underestimated the humans of that era and were defeated with their leader being killed. The invasion leader being the Queen's prized daughter, she sought revenge which led to the later Invasion of Earth.(Reborn)
Hundreds of years before their invasion of Earth the Espheni set out from their planet conquering other planets and subjugating their inhabitants. At some point they attacked the Volm's home planet which began the Volm-Espheni War and resulted in the Volm being forced to leave their planet. They now live in troop ships fighting against the Espheni and aiding all those who attempt to fight back against them. Over 100 years ago the Espheni invaded the Skitter homeworld and conquered it. Around 2011 the Espheni invaded Earth, while they have control over most of the planet, the native humans have set up a Global Resistance to retake the planet.
In 2015 the Espheni empire finally fell when the Invasion of Earth turned into a massive defeat for them. During an an attack on the Espheni base in the human capital city of Washington, D.C., resistance leader Tom Mason infected the Espheni Queen, the ultimate leader of the Espheni race, with a Dornia bioweapon. Due to the Queen having a biological link to her entire race, the virus passed into all Espheni and they were rendered extinct as were all of their creations such as the Skitters and Black Hornets.(Reborn)