The Empire of Orion was a sovereign state that existed in the Milky Way galaxy from its founding in 2612 and it dissolution 3275. It was preceded by the short-lived Provisional Republic of Orion, the People's Commonwealth of Orion, and the Republic of Orion as the legal polity of the Orion identity. It claimed and controlled large areas of the Orion, Centaurus, and upper Norma Arms of the galaxy in the spinward and trailing quarter. At its height, it ruled a little over a sixth of the known galaxy and included just under one-fifth of the human population.

The Orion Empire came into being in the early 2600s following a successful popular revolution against the repressive communist dictatorship that had been in power since the 2530s. A provisional republic existed from 2610 to 2612, when a plebiscite determined that a constitutional monarchy should be instituted on the Terran model. It is suspected by some that the Terran Empire had a hand in the results, particularly as the Orion state became an ally of the Terran Empire in the Interstellar Treaty Organization. The inaugural Emperor was John I of the House of Angevre, who had chaired the rebel leadership council and led them to victory. His house would rule the country for 160 years until its deposition by Henry, Duke of Cauvan in 2769. The House of Cauvan ruled until 3002, and the succession crisis led to a multilateral civil war between the ducal and princely houses of Gillemetz and Lao. The House of Genevra inherited the Gillemetz claim and finished the war in the late 3020s to become the final ruling house.

The Orion Empire participated with the Terran Empire in many foreign policy initiatives aimed at limiting or containing the Communist bloc led by the Soviet Republic, and at constraining the alliance of alien capitalist states on the coreward and far spinward side of the galaxy. This led to the outbreak of the Great War in 3265 when the Soviets launched a surprise attack on an Orionese colony world. The Orion military bore the brunt of ground fighting in large parts of the Soviet front and the Orion Empire annexed most conquered Soviet territory prior to 3270. The Orion state joined with the other members of the ISTO in becoming the Central Galactic Confederation in 3270, and then voluntarily dissolved itself in 3275 to join its worlds with the Republic.

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