Earliest history of Imperium Romanum is today a subject of rather... intensive propaganda efforts on behest of Imperium Romanum' security forces. However, unlike countries like The Technocracy
or Fourth Reich
, here we do possess a surviving records from other states in the region, that allow to reconstruct the early history of Roman Empire.
Long, long time a go, a certain billionaire bought a planet that, according to early cartography survey, possessed several large inland seas, with climate similar to this from Earth's Mediterrean Sea. The reason for it being a fascination of said billionaire with Roman Empire, whom he wanted to recreate, creating world's biggest open air museum.
Of course noone said anything about abandoning advanced technology. Settlers created several arcologies decorated in Roman style, sculpted their minds to better reflect what they perceived as Roman mindset (including traditional, early Roman conservatism, personal freedom, certain form of patriotism and so on). Outside of Arcologies lied lands that were sculpted to look like Roman lands, including reconstructions of cities like Pompeii, aqueducts, baths, whole fields where robotic 'dolls' could reenact various historical battles in their natural scale, and so on. Soon the planet was considered one of the most attractive tourist destination in Human Space.
Over time, the growing number of people wanted to settle it. Owner of Nova Roma – a certain billionaire who titled himself Imperator – was picky with accepting, prefering, as he saw them, 'strong' and 'worthy' people. With surprising ammounts of former soldiers and mariners from Terran Federation army and fleet included. What's more, the patriarchs that helped in settling Nova Roma and ruled its economy, soon began investing in orbital industry. After all, mining asteroids didn't influenced rural and scenic lands surrounding the arcologies.
All of this – accidentally – created a powerful basis for war industry and military, that turned out to be most useful during the Unification Wars. Soon after collapse of local Federation presence, Nova Roma was assaulted by one of its neighbours, who wanted to control local industry (and great touristic location).
That's how a spiral towards present situation began. After several years long campaign, the invader was defeated. Imperator of that time – the settler of the planet, already very old – didn't want to forcefully sculpt its inhabitants, which was deemed as only viable way of pacifying resistance of formerly totalitarian planet, where entire population was sculpted to be practically fanatic believers of their ideology. Imperator as a believer in civil liberty do not wanted to do it. Many oligarchs and army commanders wanted.
In the end, the compromise was settled – rotten as most of them in politics. Rather than sculpt them into Romans, they were sculpted into some sort of a middleground between their totalitarian and pretotalitarian sculpture... and occupied. With totalitarian part including more or less 'loyalty' or at least conformism towards those who ruled them. Soon the emperor died, and another wars happened. Some of the planets were occupied as well, some more – his descendant had less moral qualms – sculpted into Romans. As trying to sculpt the inhabitants of already conquered and occupied planet would mean facing global revolution, the status of occupation remained – at least wars end and the risk of the mass revolt will be acceptable.
Finally Unification Wars ended... but by the time, a completely new generation ruled Nova Roma. One, for which the current situation was normal. Tourism was long gone, what once began as tourist attraction started to be believe as something real. Occupied (albeit not very brutally) and exploited worlds stayed that way. After all, it was their own fault. It was them, who attacked Nova Roma.
Soon new wars begun. This time, waged not to defend themselves, but to conquer. Dream to protect themselves changed into dream of true Imperium, one that could rival the first one, the one that was discussed in schools in details. One that every inhabitant knew, and whose those more ambitious coveted. Slippery slope is terrible, because noone notices it before its too late... and those that do, are ridiculed.
Sculpts were 'improved'. Tendency towards religious indifference with small Christian influence (with roman rituals done in front of the tourists or, later, as a tradition) were replaced with belief in completely new religion, deemed properly 'Roman'. The slavery – firstly as an intendentured workers working out their debts, then as natural status of those, who weren'r Roman, from example citizens of the conquered worlds – were introduced. Each succesive generation was even more Roman in truth rather than in fiction.
Finally their conquest were stopped, their armies weak in terms of not possesing enough manpower to wage more war against its neighbours. Then, Neocrusade struck, and for the first time in long time Imperium Romanum fought for its life, and while finally succeeded in reconquering lost lands after the Neocrusade dispersed, their period of conquest ended forever.