Empire of Orion

The Empire of Orion was a sovereign state that existed in the Milky Way galaxy from its founding in 2512 and its dissolution 2675. It was preceded by the People's Commonwealth of Orion, the People's Republic of Orion, and the Republic of Orion as the legal polity of Orionese identity. It claimed and controlled large areas of the Orion, Centaurus, and upper Norma Arms of the galaxy in the trailing edge of the Milky Way. 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 2500s following a successful popular revolution against the communist government that had been in power for a century. A provisional parliament existed from 2512 to 2515, 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 Stefan I of the House of Angevre, who had chaired the opposition leadership council and led them to electoral victory. His house would reign for 160 years until the dissolution of the Empire.
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 spinward side of the galaxy. This led to the outbreak of the Great War in 2665 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 2670. The Orion state joined with the other members of the ISTO in becoming the Central Galactic Confederation in 2670, and then voluntarily dissolved itself in 2675 to join its worlds with the Republic.