Note on the Rise of the Terran Empire.
Contrary to many predictions, the United Terran Republic did not fall in a violent coup or an alien invasion. Rather, it was (mostly) peacefully dissolved into the Terran Empire. Why so? The main reason was that the old UTR was a very militarized state, born as it was out of the struggle for Terran independence from the Reticulan Empire. In its early years, the citizens of the UTR were very happy with that - they were proud of how their small, backwater state kicked out a much more powerful and much older polity and brought freedom to the Terrans. But as time progressed, and, especially, after the Second Reticulan War, these military-centered policies and attitudes became less and less popular, with their greatly inflated military budget (requiring high taxes), universal draft and strong political power held by the military.
Meanwhile, the corporations, growing rich and powerful in the wake of the Second Reticulan War and the conquest of massive swathes of Reticulan space, found this militarized setup to be a burden on their profits. So, eventually, Karl Durnhal, heir and owner to the massive Durnhal Enterprises and richer than any man in recorded history, proposed in the 2340's the Imperial system, ironically enough inspired by the conquered Reticulan Empire; it would be a mercantile society, a polity run by businessmen, by people whoi produce, who sell, who provide services, and not by militaries and their insatiable thirst for war. This charismatic vision of peace and prosperity was too much for the majority of the war-weary Terran public to resist. So, in 2345, the Act of Dissolution was passed in Parliament, dissolving the republic and installing an Empire in its place, with the ten greatest and richest megacorporation-owning families becoming Great Houses and governing space, Durnhal on top, of course. Only a relative minority bemoaned what they saw as a gross betrayal of what their forefathers fought for a century before. But the majority of Terrans rejoiced as the universal draft was abolished, the military cut back and the taxes greatly reduced. And so the Republic became an Empire. At its very heart, the Terran Empire was a glorified price-fixing scheme, a deal amongst monopolies to divide known space between their interests.
Some resisted, and, for several decades, a low-intensity insurgency was carried out by those loyal to the old Republican ideals against the Empire, but the vast wealth of the megacorporations, and the brilliant future of plenty and prosperity they promised, prevented the opposition from gaining much ground. For 43 years, the republican holdout, officially called the United Terran Republic - Emergency Administration but unofficially called the Terran Freehold, lingered on, becoming more and more authoritarian and eventually totalitarian, only to collapse under its own weight in 2388 and be absorbed by the Empire.