Fourth Era of Humanity
3400s - Artificial Gravity is invented, with inertial dampeners following up shortly, finally allowing ships to accelerate faster than two gravities without risking its crew.
3685 - The CEO of a big entertainment company based in Union territory takes a long trip in his personal star-yacht, when he stumbles upon a Imperial spyship. The yacht is quickly destroyed. But it wasn't a thorough job. Later investigations reveal a tie to the Imperium. Based on this incident, the situation deteriorates into a new all-out war. The Union is fighting the Imperium alone, while the reluctant Alliance, not wanting to drag itself into a painful, bloody conflict, supplies it from a far. The material support is not nearly sufficient and one Union world after another falls to the Imperium, dispite the preparations the Union made for centuries for a very similar scenario. The Union, weakened more and more, is fighting an uphill battle which it cannot win - after 4 months of war, it is forever destroyed as a political entity, its worlds now belonging to the Solar Imperium. The Imperium stops at that, not wishing to provoke the Alliance, which has by now colonized a huge portion of stars in the Saggitarius and in adjacent arms.
3846 - The Alliance discovers the Gondor system, which was settled in 3128 by the strayed slowship Victoria. By now the Gondorians are a race of extremely modified cyborgs, modifying their entire bodies to live in the hellish environment of their world while leaving almost nothing organic. The Alliance, headed at the time by a hawkish president, makes a half-hearted attempt at negotiation, and then invades the system in force, interested in the many riches the plentiful asteroid belts and multiple gas giants of the system have to offer. The Gondorans react to this invasion unfavorably. The Alliance troops were slaughtered in ground combat by the upgraded Gondorian cyborgs, and the space battles also quickly went in the Gondorian's favour. The Alliance retreated. It could have probably conquered the single system through sheer brute industrial output, but this invasion was unpopular enough as it was. A friendship treaty was signed between the Alliance and Gondor, and the military actions concluded with "only" several tens of thousand dead and wounded.
3849 - Gondor is officially recognized as an Alliance planet, although it doesn't hold (nor want) seats in the parliament or any political influence. The Gondorians, dispite being primarily miners, are sometimes hired as elite Mercenaries and they perform the job of a soldier admirably.
4149 - For the first time ever, a living alien civilization is discovered. The aliens are primitive spear-throwing stone age savants, but they nevertheless posses a rudimentary culture, language, folklore etc. They are secretly studied by Alliance researchers, without revealing the existence of Humans to them.
4302 - A second primitive alien civilization is discovered, this time a decadent Bronze-age civilization. They are studied in a similar manner to the first alien group.
4373 - The Imperium, having been space-locked for many, many centuries without any hope of expansion, has prepared and armed itself continualy ever since conquering the Sovereign Union. When a couple of planets, for some reason attracted to the Imperium's evil ideology, decide to secede from the Alliance to side with the Imperium, the Imperium acts. The Alliance, naturally, couldn't let two planets go over to the Imperium. That would've established a bad precedent, as well as making the Alliance look weak (nevermind that merely two planets were not enough to damage the Alliance neither militarily nor economically). The Imperium latches onto this excuse to follow up with an extensive fleet sent on multiple fronts, and starts the Third Inner War. Initial engagements go to the Imperium's favour, but soon the war machine of the Alliance heats up, and the Imperium starts to feel what it's like to tackle a behemoth.
4374 - In the Alliance's counterattack, all the planets the Imperium annexed since the beginning of the war were liberated. Not only that, but the Alliance has invaded into former Union space, popping one Imperial outpost after another, sending angry swarms of infantry down onto the entrenched defenses of the Imperial planets. The Alliance manages to conquer a large swath of territory, but are bogged down in the guerilla warfare the Imperium utilizes against them. They decide to withdraw from all former Union planets. The Third Inner War is concluded In a little over a year since it started.
4547 - A peculiar phenomenon is accidently discovered on one frontier planet. Its entire continental mass is deeply covered by black-colored plants, so densely that the continent seems invisible from space even during daylight (black against a black background). Attempts to land probes were a total failure, as the plants seemed to absorb all electricity from both electronics and organic beings. Attempts to shield the unmanned probes from these effects have all failed, and the phenomena remained unexplained.
4690 - A second "Black planet", covered in identical plants, is discovered in a location very far from the first one. Scientists are completely puzzled. Theories about "space plagues", "evolutionary peak" and others start to pop up.
4702 - On a newly colonized planet, the Alliance discovers a very ancient, long abandoned alien spacecraft. They discover a starmap describing the several colonies these aliens had in this part of space. Other discoveries yield great technological innovations in propultion system, going from fusion to Ion drives, giving Alliance ships greater acceleration, and a primitive Maggot-drive. An especially elite team from Napoleon is sent to study these far away planets.
They find long-burried ancient colonies, but when one of the teams reaches the planet later to be known as Pandora, they find only a single structure unlike anything seen before. They're attempting to cut through it, but the metallic reddish substance it is made of isn't even scratched by their best efforts. Eventually they find an entrance. Inside, they walk around various corridors filled with very alien-looking machinery, when the AI defending the structure activates itself, captures the team, and begins studying them while they are placed in a state of stasis.
4713 - After the dissapearance of the Pandora team, a second team is sent to discover what happened, and if possible to continue their mission. Most of the team is composed of Gondorian cyborgs, who are supposed to provide protection against any threat that might have killed the first team. The second team's fate is exactly identical to the first's. Shortly after the second team's dissapearance, Pandora system is declared a quarantine zone.
4800 - The alien Mastermind finishes studying his human subjects. Both teams are released, but they are not what they've been before. The computer has made subtle alterations, also in physiology but especially in their mentality. They are now loyal subjects that will carry out the Mastermind's whims. The teams return to their preserved spaceships, and leave to Alliance space.
The teams form cults that worship the Brain Prophet. Through cunning manipulation and plotting, they get their hands on large sums of money and begin to gain followers. These cults, after a short time, gain mysterious access to very advanced technologies, due to the knowledge ingrained into the minds of the team members.
5000 - The cults have by now spread their influence greatly among the stars. Still led by the same people, their age process slowed down thanks to obtained alien technologies, they have grown into mighty religions in their own right. These cults also own large corporations that sell highly advanced technology, which are, in truth, alien-derived. Such technologies include a medical chip, that is widely used within the Alliance. It is implanted into the brain at birth, and monitors the health of the human right until his death, picking up even genetic defects. Little do the innocent people know, it also has a hidden function...
5002 - The cults are ready to act. Suddenly, armed cult members seize key positions in the Imperium and Alliance. Medical chips on the inside of billions of human skulls hum to life, creating a FTL link between the human brains and the Mastermind, using technology far ahead of Megawaves. These people are instantly turned into loyal members of the cult, which is now proclaiming the formation of the Hive, that will "set the human race onto the path of ascention". The coup is sucessful in the Alliance, but the ruthless Imperium, hardened by centuries of rebellions, uprisings, riots and guerilla fighters of surviving ethnical minorities, manages to hold off the mad armies of cultists. The standoff lasts a week, and then, under very mysterious circumstances, the Solar Authority's forces in space are unexplicably destroyed. With space superiority firmly in their hands, the Hive completes its job. A mass program of chip implantation begins. The final goal - a complete 100% implantation of the human race with link-chips, that will turn them and their children into puppets for the rest of their lifetime.
The General Planetary Alliance and the Solar Imperium were dead. All that remained was the Hive.