The Webway(aka the Labyrinth Dimension) was a realm created long ago by the old ones. This place was completely safe from the forces of chaos, and was inhabited by the Aeldari. The Big E was about to pull a “Here’s Johnny!” On the Aeldari and take some of the Webeay for humanity. This allowed the newly corrupted Horus to do naughty list warranting things. Now, back to the other Primarchs. Magnus the Red(not a traitor yet) knew about the betrayal of his brother, and psychically projected himself in such a brain-shattering, migraine inducing way… that it broke the barrier against chaos on the Imperial Palace on Terra. Now, I’m no shield genius, but I’m pretty sure a broken shield is no good. So, daemons did daemon stuff and killed thousands of people fighting them off. The Emperor was stuck on the Golden Throne. His greatest tool, was now his strongest prison. Big E was not happy about his naughty red rascal, so he sent the Executioner Primarch. Leman Russ the 6th Primarch, general of the Space Wolves. During the Battle of Prospero(the planet Magnus did his video call) was kinda silly. To protect his sons from the Space Wolves, he used bad spells, and got snatched up by Tzeentch. He is now a chaos Primarch boo hoo. But Horus needed more of his brothers. He recruited Fulgrim of the Emperor’s Children, Mortarion of the Death Guard, and Angron of the World Eaters. A ship escaped however, and told the good fellas about how Horus was being a brat. Horus knew he could not fight the rest of his brothers at once, so he kept them busy with wars across the galaxy. The first wave was on Istavan 5, and was met by Ferrus Manus of the Iron Hands, Corvus Corax of the Raven Guard, and Vulkan of the Salamanders. The second wave came from behind them. Arriving were Konrad Kurze of the Nightlords, Perterabo of the Iron Warriors, Lorgar(fricken hate Lorgar) of the Word Bearers, and Alpharius of the Alpha Legion. The loyalists were not prepared for this. Thus it gained the name, “The Dropsite Massacre”. Now they are evenly matched. 9 traitor Primarchs against 9 loyalist Primarchs. But three legions were severely weakened, and the Primarch, Ferrus Manus, was dead. Horus still knew that he wasn’t strong enough to fight his dad, but then he found it. The Warp Gateway at Mo. he went in it and gained the favor of all four chaos gods. This made him pretty strong. Something important happened a while after. The 9th Legion Primarch, General of the Blood Angels, the Great Angel, Sanguinius, was in charge of human war stuff now because Horus is a bad boy. This includes the giant war machines called Titans( or God Engines). The Mechanicus praised these things like gods. So this part of the Heresy is important. This was the first major event on the Siege of Terra. He commanded the war machines to fight the other traitor war machines. This led to the titans on both sides dying a lot. This was called the Titan Death. Titans are ancient technology from before the Age of Strife, so we can’t make more. Anywho. Three loyalist Primarchs were able to fight at the Siege of Terra. These were Rogal Dorn of the Imperial Fists, Jaghatai Khan of the White Scars, and Sanguinius, beloved by all, of the Blood Angels.(I love Sanguinius so much no like actually I love him more than 13 year old girls in America love Taylor Swift).