Kryptonian Hegemony
The Kryptonian Hegemony exploded out of nowhere ca. 50,000 BCE and became an overnight threat to much of the galaxy's civilized life.
Krypton was a single-planet population for millennia, with a thick atmosphere and dense heavy metals suspended between air layers. The galaxy was unaware of early Kryptonians as anything except a sub- Type I civilization. Many species took decades or centuries from their first space flight to their first interstellar colonies. When Kryptonians first launched themselves into space, they were outside of their atmospheric barriers for the first time. Exposure to solar radiation triggered a cellular reaction that supercharged their bodies with unparalleled power.
In the space of fifty years, Kryptonians had conquered a dozen neighboring sectors and were engaged in full-scale war with Oa and many other species in adjoning star sectors. They seemed utterly invulnerable. Only the mightiest of weapons and individuals seemed to do them harm, or even slow them down. They expanded their empire rapidly, under the auspices of a political theory called "The Great Inquiry", in which Krypton would introduce peace and civilization to neighboring worlds-- by force, if necessary.
The Hegemony consolidated their scattered operations into a military operation and directed aggressive campaigns against any resistance. Even the least of Kryptonians possessed vast strength, invulnerability, and independent flight. When they blew away the heavy metals obstructing their primary sun, every Kryptonian became empowered as never before. With their increased perception came increased intelligence; Kryptonians realized that glittering sunstones worshipped by primitive tribes were natural conductors of the same cosmic radiation that empowered Kryptonians. These sunstones were naturally-occurring versions of the same crystals that served as the backbone of advanced technology across the galaxy.
A single Kryptonian was an army. Ten of them in one sector was a war crime. Needing little materiel to begin with, the Kryptonians soon found they could fly across the stars without even needing spaceships.
Vast coalitions of spacefaring races tried to resist the Kryptonians, particularly Oa. The Hegemony destroyed the Manhunter Robots in legion, a single Kryptonian a match for dozens of those potent machines. All was to no avail, and it seemed likely that Kryptonians would conquer the whole of the known universe if not stopped.
Oa, their chief rivals, attempted multiple gambits to stop the Kryptonians. The first was the formation of the Green Lantern Corps, more flexible and cunning than their Manhunter robots. The second was to irradiate entire galactic sectors with wavelengths of energy known to be hazardous to Kryptonians. The third was to create an army of warriors, physical equals with Kryptonians but armed with magical weaponry. For this, they turned to the Demiurge, a proto-sapient mass of energy in deep space, and the refugee First Gods living there. Together, Oa and the First Gods pushed the Demiurge into true self-awareness, and from that evolution came the hawkish, proud warrior kingdom of Asgard.
Finally, Oa's long-term gambit: a genetic plague, slow incubating and difficult to detect. Krypton did not know it was poisoned until fertility rates abruptly reached 0%. In the space of a decade, no new Kryptonians were born, to a species with an already low birth rate. In the space of a century, the Kryptonian population dropped by 99% due to war and attrition. They huddled on their home world of Krypton to try and find a solution. Oa seeded their orbit with irradiated rocks formed from chunks of a neighbor planet, creating a web of "Kryptonite" that prevented independent space flight. Krypton's primary star, Rao, was fed destabilizing matter in an attempt to get the red giant star to implode.
Krypton turned to science, and the few survivors rapidly made up for centuries of their intellectual dark ages. Though they were unable to repair the damage to their main star, they built domes that mitigated the worst of the lethal Kryptonite and used genetic therapy to sustain the species with new Kryptonians. The most desperate even used cloning techniques that had been outlawed since time immemorial. For thousands of years they limped along, frequently subverted and sabotaged by Oa. Even their attempts at technology were stymied-- their Brainiac AI was corrupted and sabotaged shortly after flying off-planet, becoming a dangerous threat to much of the universe's life.
Jor-El: The Superman
In the end, one Kryptonian scientist made a desperate gamble. In approximately 1918 CE, Jor-El boarded the last of their hyperspace ships to try and locate the ancient cousins of the Kryptonians: the Kherans.
Malfunctioning equipment led Jor-El not to Khera, but to Earth and the nation of Wakanda, and their reserve of the Heart-Shaped Herb. It was in the blood of Wakanda that the solution could be extrapolated, and the scientist hurried home with his discovery in hand.
Jor-El and his brother were able to use the gene therapies and help their wives conceive one child each. Kara Zor-El was born first, and her cousin Kal-El was born some thirteen years later.
For a brief moment it looked as if the Kryptonians might survive. A race brought low, allowed to return to life and flourish once more.
It was not to be. Krypton's time had come, and their planet's doomed star was rapidly destabilizing due to Oa's machinations. The House of El worked frantically, modifying Jor-El's spaceship into a pair of emergency hyperspace pods. The cousins were placed into them, Kara admonished to care for infant Kal-El. Kor-El set the coordinates for the only safe place he could think of-- Earth. A primitive backwater near the Great Void at the center of the universe, far from the machinations of Oa. The only place in the entire cosmos where the House of El was honored and respected.
Moments after the cousins escaped Krypton's orbit, their star Rao went nova. The legacy of Krypton would live on largely only in memory from that point forward.
