The Emperor knew he could not do this on his own, so to unify the Sol system, he and his closest friend and his most trusted ally became the Three Musketeers of humanity. The smartest Perpetual and strongest psyker to ever exist, Malcador the Sigilite was his best friend. And Erda, the master bio engineer. They knew they needed a strong, mass produced kind of soldier. One that was stronger and faster than the others. They created the Thunder Warriors. With the Warriors they easily unified the Sol System. But the interesting part is when the Emperor went to Mars. Mars, as a matter of fact, had developed something called the “Mechanicum” I cannot bring myself to describe how horrifying the changes they made to their body were. But imagine cyborg made less modern and not pretty. Remember the C’tan? One of them landed on Terra. The Emperor did not like this. So he banished the Machine Dragon to Mars. The Dragon gave some of his power to the machines on Mars. The Mechanicum believed that this was a “Machine Spirit” so they became the ultimate tech dweebs. Like, they prayed to their guns so they would work. They even created the most powerful weapons of all humans. They created the hulking God Machines. These walking giants had the power to lay whole cities to waste in seconds. Most people however, simply call them Titans. Now, one of the Titans weren’t working correctly. When the Emperor went to Mars, they were skeptical of his power. But then he found the broken Titan, simply touched it, and it was functioning again. Mars then became the first forge world of the Imperium. Enough of that now. Let’s go back to war. The Emperor knew that the rest of the galaxy had more humans to unite, but Thunder Warriors weren’t enough. He needed more Perpetuals. Artificial if you will. The Primarch Project went underway. On one planet I forgot the name of, there was a gate to the Immaterium. Some say the Emperor went in and made a bargain with the Dark Gods. Others would say that he stole their fire. When he emerged from the portal back into realspace, he was more powerful than ever. He had gained the knowledge to create his sons. So he did. He created 20 Primarchs. But during the incubation process, somehow, they got into the Warp and were scattered across the galaxy. Not important how I’m not getting into that it’s too much even for me. Anyways. Even with the Primarchs missing, he could still unify humanity. The Thunder Warriors would have been fine. If it were not for them losing sanity in a few standard years. He needed more. Stronger, smarter, and faster soldiers to be mass produced at a much larger scale. The Space Marines were born. 20 legions of gene-enhanced soldiers to go with the 20 Primarchs. You get the gist of it. He conquered more like he does. But then, he found what he had been looking for after so long. Horus Luprical, the 16th Primarch was found.