Last time I left off with mankind having fallen into the Age of Strife, which was a bummer of a time for everyone!
Today though I will take us out of the Age of Strife and up to the Great Crusade.
In the 25th millennium mankind was split up and at war with itself and countless alien species. Planets were cut off from one another by terrible warp storms and human psykers were becoming gateways for infernal creatures from Warp Space. Mankind was at the brink.
On Earth a myriad of petty warlords arose and created their own kingdoms. Most of these warlords were simply power hungry men who were powerful enough to subjugate those unfortunate to be close by. However a few of these were truly evil men, such as the Pan Pacific Tyrant Narthan Dume, the Unspeakable King, and the Seven Neverborn who brought about horrific atrocities that went so far that soon there were far more dead on Earth then living.
Not all of the men were evil. One would later be known as the Emperor.
The Emperor created an army of Thunder Warriors, genetically superior warriors armed and armored with the best technology that had survived Old Night.
Once Earth was reunified the Emperor had to undertake drastic steps to save his race. The radiation of countless nuclear wars had severely ravaged man's genetic structure. Humans of this time would hardly be recognizable as such to us today.
Using his research from creating the Thunder Warriors the Emperor was able to stabilize the human genome. The Emperor wasn't done however. Saving man from the radiation wastes of Earth would not be enough. Mankind needed to reclaim its place in the galaxy and while the Thunder Warriors had been enough to reclaim Earth, they were too rough a product to mass produce to conquer the galaxy.
The Emperor began the Primarch project. 20 individuals created from the Emperor's own genetic code, each would sire a legion of genetic super warriors that the Emperor would use to conquer the galaxy in a Great Crusade.
The Great Crusade and the Horus Heresy!