They knew of this invasion decades ago. They held the evidence and kept it secret for over 70 years. They can't say we didn't see them coming. Our telescopes and satellites picked up their fleets at the edge of our solar system and still we did nothing, governments and their corporate backers preferring to just ride it out instead of alarming and arming the populace. They knew, and did nothing....
Their great ship first appeared as a comet, but as it neared Neptune we knew it was no comet. At the height of our civilization they came, to conquer and exterminate. They came for our water, our oceans, rivers, lakes, streams, even the water in our own bodies. Tokyo, New York, London, Paris, Moscow, Rome, Beijing all destroyed by the invading hordes. They didn't bomb us from orbit or send their ruin down like rain from the sky. No, they sent their troop ships and took our water, our cities and our very lives by force.
The only glimmer of hope to emerge from this happened in Los Angeles, CA. The United States military, led on the ground by a heroic Marine Sergeant, fought a brave retreating action there and brought down the first of the great troop mother ships. Word of this spread like wildfire around the globe and soon the invaders were retreating. But for how long? Was it a retreat or a regrouping? As a species we could no longer sit back and stare at the stars and wonder. It was time for action, a time for us all to unite or die off. With millions dead and great cities leveled, the survivors began to blame their governments, religions and corporations for the devastation. Being human, they could not unite as one. However, wary of a return to the days of corporate greed and ignorance, they formed into two groups, the United Earth Federation and the Grand Soviet Republik. The UEF on Earth was originally comprised of North & South America, Western Europe and Africa. With the GSR controlling Eastern Europe, the Middle East and Asia.
In the 300 years since that fateful time, mankind has bravely sailed the heavens in search of colonies and new threats. Ever on the lookout for the fell creatures that invaded our home those many years ago. Alien contact would be made again and again, however with less disastrous effects as the first, even peaceful beneficial contact was made. Despite this we never forgot where we came from and why we first took to the stars. Yet despite an alliance to assist in the event of another Xenos war, the humans of Earth continued to war against one another throughout the years. Being human, new factions emerged, colonies rebelled and religions grew militant. The race now controls a small part of the Milky Way galaxy, with the major players being the UEF, the GSR, the Holy Malvernis Empire, and the Tau-Ra Collective. The Tau-Ra Collective is unique in that it is the only major power that counts Xenos among it's citizens.
Of course there are many lesser factions among the stars of the Milky Way, including human pirates, petty planetary baronies, lawless frontier planets and asteroids, rogue drone infested stations and satellites, and self-sufficient human colonies aboard giant space stations and manufactured moons.
Yet despite all of our discovery, growth and contact among the stars, there is one theme that unites us all, even the Xenos we've since contacted share this one thing with us. Fear; fear of the return of that dread comet, the Comet Empire.