Cellean Culture

The Cellean autocratic space was a very major power and important historical player in the area it existed in, roughly in the 200-250 lightyears from Earth region, on the then-outer rim of human space. A its height, it held dominion over 12% of human space, and around 5 trillion people. The culture they practiced also spread throughout, though loosely.

"Cellea was burned to the ground long ago. Its memory remained for quite a while in the empire's followers, but the decision was made to relocate the capital to a more advantageous position. Whether that was a good decision is debatable, but those savage warlords, scavengers seeking but a piece of the glory of Cellea burned it again in their wars. They will never reclaim the Cellean throne."

— Stringer

Cellea Itself

The empire's first planet proper, Cellea, was a barren rock like so many others. Unlike those others however, it has had water in the past, at some point. A lot of that water was still around, mainly in icecaps upon the frozen world, around Earth's distance, but around a much dimmer pair of stars, Janor and Mosi. Nowadays it is a scorched rock, devastated by several wars and raids over the centuries.

History

Cellea is a first-generation settlement, meaning the original colonists came directly from Earth. They were sent aboard the Orgullo De La Cuna (eng. Pride of the Cradle), a particularily large colony ship with nearly five million population. This allowed them to retain and develop new technology, keeping the edge that was a major part of their success. The high tech and population was instrumental in establishing their industrial base, the other major part of the Cellean empire's supremacy.
A rough timeline of the Cellean people, and their empire. It's also down there, next to metadata.
The history of the Cellean people follows the Cellean autocratic space's history nearly hand-in-hand, so I'll be summarizing the later events.

Collapse

The Cellean empire was a spread-out state in the extreme. Its fleets left little more than a token defensive force after conquering a solar system, and moved on, often slightly diminished in strenght. A large majority of these fleets would come to a dead stop, often via a gathering of forces from unconquered systems who had a head start, or other major players, like the ASTUN. These fleets would often be crippled beyond operational capacity, or outright destroyed. News of a defeat like this would reach the ears of nearby conquered settlements, which would often revolt or otherwise split from the empire, now with no fear of retribution. News of these revolts would reach other systems in a few years' time, and so on, like a wave through the empire.
Eventually, most of the empire was gone. The central areas remained intact for longer, due to being easier to reinforce and defend, and having more people who are truly part of the empire, but eventually those caved too, as newly formed warlord and remnant factions began to fight within themselves.

"There remains little of the Cellean empire today. Even their culture, accounting for normal cultural shifts, has almost been eradicated in its old form."

— Knsa Lorian, 2754, The Outer Empire

Culture

Cellean culture was very militaristic, and very warrior-like. The Admiral-Captains of Cellea, leaders of Cellean fleets, were not only accomplished and intellegent commanders and leaders, but also skilled combatants and warriors. Many often lead from near the front, if not at the very front.
They also had a sizeable sense of superiority over others. It wasn't entirely unfounded, as most other nations in the region were less advanced, developed, or just younger. This attitude was reinforced even more when their conquests started to really pick up, and many remnants share the sentiment of superiority, even to other Cellean remnants.

Spread

As the Cellean empire spread, it spread its culture along with it, suppressing or integrating local cultures, and converting them to follow at least surface-level Cellean practices. This included the militarism, which was part of the fleets being able to reinforce themselves. While most nations kept to their own cultures, they at least integrated some traditions into themselves, which are visible today.
The area this cultural influence reached was roughly equivalent with the Cellean state's reach. Around the rim, counterclockwise and slightly downward in the galactic plane, and anywhere from 120 to 250 lightyears from Earth. The culture also spread to new colonies established after the collapse, be they refugees, exiles, or just settlers looking for another place. In fact, colonies like Ak'Thakra with no Cellean heritage are abnormally rare in the region. A good signifier as to whether or not a nation is Cellean-influenced is to look for specific traditions, especially military ones like Shoulderpad allegiance denotion.

Tech level

Being a first-generation colony with the capability to develop technology even in-flight, as well as a rare direct feed of information from Earth, Cellea, when founded, was a colony with roughly 2250s-level tech while Earth was at the 2300s-level. They were advanced. And those advanced remained and were developed further, even after contact with Earth was cut. In fact, at the height of the empire, their technology was equivalent to Earth and the core, albeit some aspects less developed and others more. For example, the Cellean Autocratic Space had more efficient interstellar travel, and better Mass Drivers. That level of technology is now largely lost, and the remnants of it fought over by ambitious nations and splinter factions.

Modernity

To call what the Cellean Autocratic State left behind a power vaccuum would be the understatement of the century. The collapse had left behind countless states, now independent, with various goals. Other sought to defeat each other, others wished for peace but could not achieve it. Nearer to Cellea proper, there sprang many warlords, each seeking to reclaim the remnants. Whatever their goals, the majority would end up in conflict eventually. To that end, Cellean relics were highly sought after. Old fleets, near-decommisioned ships, caches of advanced weapons, an industrial area, even a small shipment of medicine and life-extension treatments was invaluable in the farther regions.

"Now we've hit it boys, a good and proper old Cellean cache! What's this, a couple coilguns, some cannons, some medicine, prosthetics... Yeah, this'll fetch a nice price back on Jorangor."

— Kalen Smithe, 2821

Origins

The original colony ship was composed mainly from people living around the Mediterranean, especially the northernwestern sections. With that, the dominant ethnicity within the population was spanish and southern french.

Language

The official, though poorly enforced, language of the Cellean empire came to be known as Old Cellean. It started as a mishmash of Spanish and French, and over the long flight gained a heavy influence from Latin. While nowadays the language is dead, only spoken by a comparatively miniscule amount of people, stuck in the 2600s, it had became a heavily latin-influenced tongue, with many more influences from elsewhere.