The Early Days
In the beginning, all of humankind lived on a single world, drifting through space: Earth. Billions of humans squabbled over her wonders, until it seemed the planet could take no more. And then, humanity opened the gates to the stars. Millions of ships pored forth from Earth, scattering amongst the stars in a mad scramble for resources. From this chaos spawned a multitude of stellar nations; a thousand petty empires squandering lives and resources in meaningless conflict. As time passed, some of the nations grew stronger even as others fell in the crucible of war. Humanity's first encounters with alien civilizations were a massacre: the aliens fell swiftly before mankind's wrath. It seemed like humanity's place in the universe was assured.
The End of an Era
...But it was not so. As Mankind's reach expanded, it eventually came into contact with an impossibly powerful alien civilization. These nameless aliens came to mankind not in search of conquest, but to 'convince' Man to join in their interstellar civilization: the Colturi; Colser in the tongues of men. A name that would swiftly become the most bitter of curses. The influence of this alien culture spread throughout human space like a cancer, eating away at the works and dreams of all mankind.
Over time, untold millions of humans left to join the Colser. Some were lured by their wonders, some by the promise of freedom and power, while others joined simply to escape the crushing despair that comes from seeing an alien destroy, or worse, duplicate, your entire life's work with but a wave of their hand. Faced with the growing irrelevance of their works and slow the slow attrition of their citizenry, the great star-spanning nations of Man faded. All seemed lost.
The Coming of the Prophet
And then salvation came. A vessel emerged from Colseran space. Aboard that ship was a man, his mind bursting under the weight of his revelations. He had been to the very heart of the Colser; he had walked their roads and danced their dance of endless excess, and found it all hollow. He had seen their gods, and learned of the true nature of man’s fight. And he saw a path to victory; a Way that lead to humanity’s salvation. The man told humanity of the inhuman truth of the Colser, of the twisted and disturbed things they turned to to amuse themselves, of the way that, by having everything handed to them on a silver platter by their machines, they had lost any true accomplishment. He spoke the words that mankind most needed to hear; that, for all their wonder, the Colser's works ultimately were for naught. That there was a path to follow, a Way followed by the Architects whose works were wrought into the very shape of the galaxy, and that the Colserans had lost it. And that humanity could follow it.
He said that there was hope.
And mankind heard. Slowly, the man's words and his Way spread across human space. This man was the Prophet of the Way, and mankind clung to his words as a drowning man clings to driftwood. Slowly but surely, he gathered followers and devotees, bringing hope to all of humanity. His words began to knit together a common dream for all of human space; a dream where man overcame the temptations of the Colser and assumed a place of greatness in the galaxy.
And then he was cut down in his prime by the cowardly enemies of mankind, the bright star of his life extinguished by gleaming robotic hands and cold strategic algorithms.
The Church of The Way
And yet, the Prophet's dream lived on. He had forseen the possibility of the Colser attempting to destroy him, and so he had founded a mighty institution to carry on his works for all mankind: the Church of Terra Ascendent. The Church was to deliver the Way of the Prophet to the people, ensure that they did not stray from the path, and to be their rock against the depredations of the Colser. But in order to do all of this, the Church would need to be a bastion against the temptations of the Colser. Temptations which only a single man had ever overcome.
The early Church toiled long and hard at this problem, before finally coming to a difficult solution; the Prophet was to be cloned. Each new Prophet that emerged from the Church's vats as an infant was to be raised and taught the ways of the Church, pouring countless hours into careful examination of the Prophet's writings. The majority would then then spread out amongst mankind to continue the First Prophet's works, while a select few would be sent into the Colser to repeat the Prophet's great ordeal in a desperate attempt to recapture his Lost Revelation--the goal of the Way. Those few who have ever returned have been twisted and warped beyond recognition by the Colser in a desperate attempt to 'convert' them. This system persists to this day, ensuring that, while Emperors and Lords may fall to temptation, humanity will always have a rock on which to depend.
The Imperial Republic of Centaurus
Over the ensuing centuries, the Church grew. And, as it grew, it began to pull the petty empires of mankind together under the Way. Eventually, under the guidance of the Church, the secular leaders of mankind agreed to unite their military power under a single banner. Each of the stellar nations which made up human civilization was transformed into a Noble House under a newborn Republic. Each of these Houses would send a representative to a ruling body known as the Landsraad, who would then elect an Emperor to lead the Republic's military forces. The first act of this Republic was to erect a massive administrative Ring-Station around the Centauri Triple Star system, thus giving the new republic its name: the Imperial Republic of Centaurus.
The Armies of Humanity
The Imperial Republic's possession of the Way has won them many enemies, human and alien alike. To fight these enemies, and safeguard the future of all humankind, the Imperial Republic has gathered a mighty army under the Imperial banner. Billions of brave men and women from the Noble Houses are drafted into humanity's armies. And from them, the best and brightest are selected to become something more than merely human. Enhanced by potent cybernetics and clad in the nigh-impenetrable Nephilim-Class Powered Armor, they stand side by side with genetically engineered supermen grown and trained by the Church as Stellar Knights; as the pinnacle of humanity's fighting forces, avenging angels sent to destroy man's enemies.