Empire

An empire was a state which controlled more than one culturally distinct population groups. These were often different planets and/or species. Empires were usually led by an emperor, (TV: Nightmare in Silver) or empress, (TV: Empress of Mars) who could be elected or hereditary.

The First Doctor told his companions Vicki Pallister and Steven Taylor that every empire in the history of the galaxy eventually collapsed. (AUDIO: Upstairs)

Human empires
There were many empires through time and space. Earth itself had several empires in its history. One of its earliest known empires was the Roman Empire, that centred in the city of Rome. (TV: The Big Bang) Although it eventually fell, (TV: Day of the Moon) it would later come about again as the New Roman Empire, a civilisation that flourished around the year 12005. (TV: The End of the World)

The Huns ruled a vast tribal empire centred around the region that would later become Kazakhstan. (PROSE: Combat Magicks)

The largest Earth empire encompassed by a single nation was the British Empire, the empire of the United Kingdom which spread across the Earth. (TV: Tooth and Claw, The Empty Child, Empress of Mars, Demons of the Punjab) By 1850, it was considered the most powerful empire in Earth's history up to that point. (AUDIO: 1963: The Assassination Games) The nation of Japan also had it's own empire, which was the prominent power in Asia during the first half of the 20th century. (PROSE: The Shadow of Weng-Chiang) The Empire's ultimate aim was to unite Asia under the Asian Co-Prosperity Sphere. (PROSE: The Face of the Enemy) The Japanese and British Empires fought against each other during the Second World War. While Japan initially succeeded in taking Britain's colonies in Singapore (AUDIO: The Forsaken) and Burma into it's own empire, (PROSE: Just War, The Scales of Injustice) Britain (serving as part of the Allied powers) ultimately proved victorious in the conflict. (PROSE: Magic of the Angels)

Humanity also grew to eventually have galactic empires. While the date is uncertain, the first official Earth Empire formed in either 2501 by EarthGov, (PROSE: The Monsters Inside) or 2530s, by the Earth Federation. (PROSE: The Colony of Lies) By around the year 4000 (TV: The Daleks' Master Plan) the Earth Empire's successor, the First Great and Bountiful Human Empire came into being (AUDIO: The Lost Flame) In the 42nd century, the Second Great and Bountiful Human Empire had influence in the Tri-Galactic. (TV: Planet of the Ood) Humanity later developed the Third Great and Bountiful Human Empire, which described the Eleventh Doctor as "neither great, nor bountiful, nor overwhelmingly human". (COMIC: A Fairytale Life) They also had a Fourth Great and Bountiful Human Empire that was manipulated by the Daleks. (TV: The Long Game, Bad Wolf, The Parting of the Ways) By the year 5000000000, The New Earth Empire (the official successor to the original Earth Empire) was created and governed by humans across the earth. (COMIC: Agent Provocateur)

Humanity was also once directly controlled by another alien force,, who formed the New Time Lord Empire, with the Toclafane acting as his army to rule over earth during the Year That Never Was. (TV: Last of the Time Lords)

Earth's empires also did battle with other alien races. One notable example is the Draconian Empire which was the interstellar empire of the Draconians. (TV: Frontier in Space) The Fourth Great and Bountiful Human Empire also fought and lost against the Daleks. (TV: The Parting of the Ways) Emperor Ludens Nimrod Kendrick Cord Longstaff XLI, Defender of Humanity and Imperator of Known Space, led his human empire in battle against the Cyberiad, a Cyberman empire. (TV: Nightmare in Silver) In 1881, soldiers from the British Empire (serving under Queen Victoria, Empress of India) fought against the Ice Queen Iraxxa on Mars, where she attempted to revive her empire of Ice Warriors. The conflict ended with the humans and Ice Warriors forming an alliance. (TV: Empress of Mars)

Alien empires
Species beyond earth also created their own empires.

The Daleks had their own Dalek Empire, a time- and space-spanning empire created by the Daleks. It served and died in the Last Great Time War. (TV: Dalek, The End of Time, The Day of the Doctor) After the war, Davros created a New Dalek Empire, which was eventually slaughtered by the Meta-Crisis Tenth Doctor. (TV: The Stolen Earth/Journey's End)

The Sontarans had their own Sontaran Empire. (TV: The Sontaran Stratagem, The Poison Sky) They held a deep rivalry with the Rutans, (TV: The Sontaran Experiment) who had their Rutan Empire, the hive minded empire of the Rutan Host, ruled by the Rutan Queen.

The Cybermen had their own Cyber-Force, the overarching collaboration of their forces.

The Logistomancer ruled over A32K, a cold empire of logic, for ten thousand years. (PROSE: Cat's Cradle: Time's Crucible)

The empire of the Chelonian race of Chelonia was called the Chelonian Empire.

The Levithia was one of several planets aligned in the Cyrrhenic Empire. (TV: The Ribos Operation)

The immortal alien tyrant known as Horath ruled over the Dark Empire. (TV: Enemy of the Bane)

The Eleven-Day Empire was created by the Faction Paradox from the lost eleven days — 2 September through 14 September 1752. (PROSE: Interference - Book One)

The Fledgling Empires was one of the earliest interstellar empires in the universe during the Dark Times. (TV: The Runaway Bride)

The Gubbage Cone Empire was the empire of the Gubbage Cones.

The original empire from the planet Manussa was the Manussan Empire. (PROSE: Snakedance)

The Morok Empire was the empire of the Morok race. (TV: The Space Museum)

The Selachian Empire was the empire of the Selachians. (PROSE: The Final Sanction)

The Shagrock Empire was a major force in Mutter's Spiral. (AUDIO: Bang-Bang-a-Boom!)

The Skonnan Empire acted as the governing body of the Skonnans which controlled hundreds of planets. (TV: The Horns of Nimon)

The Slow Empire was an empire established millions of years ago by a humanoid race of unknown origin. (PROSE: The Slow Empire)

The Sumaran Empire was created by the Mara. (PROSE: Snakedance)

The Dominators ruled the Ten Galaxies with their Quark servants. (TV: The Dominators)

The Threllip Empire was the governing body of the Threllips. (AUDIO: Living Legend)

The Tragellans had a governing body known as Tragellan Empire. (COMIC: Beneath the Skin)

The Traken Union classed as an empire. It consisted of a group of five or six allied planets centred on the star system of Mettula Orionsis. (PROSE: Divided Loyalties)

The Tymerian race's leader, her Royal Tectrope, ruled over the Tymerian Empire. (PROSE: Forever Autumn)

The governing body of the Ulians was called the Ulian Empire. (PROSE: The Doctor on My Shoulder)

The Knights of Velyshaa created the galactic Velyshaan Empire from Velyshaa. (AUDIO: The Sirens of Time)

The Wurms had their own interstellar Wurm Empire. (PROSE: The Art of Destruction)

Behind the scenes

 * According to non-narrative info in DWBIT 47, the Daleks had a Second Dalek Empire.