What Does It Mean That Guilliman Founded the Second Empire?

When the Emperor arrived at Macragge, he originally expected to find an ordinary son of the Primarch just like he found Lion and Russ. Emperor: "What does it mean that Guilliman founded the Second Empire and became the Emperor? Magnus is his master? Angron is his Warmaster? Perturabo is the Minister of Science and Research? Lorgar Aurelion is the Minister of Propaganda? Connor de Curze is the Grand Inquisitor? Mortarion is the Minister of the Interior? Fulgrim is his Advocate Commander?" Ryan: "The ambitious Guilliman will rebel, and we will have a battle with the Second Empire." Malcador listened to the information from his assassins: "What do you mean, Guilliman used the technology of the Old Saints to build a webway city under Macragge, and is now laying the webway across the galaxy?" Horus couldn't figure out how the mediocre guy like Guilliman got so many brothers to pledge their loyalty to him. Guilliman wears Gothic gold power armor, holds a flaming sub-organism sword, and has a red cape flying. Guilliman looked at the group of Primarch brothers and 800,000 Imperial Guards standing behind him, and said to the Emperor in embarrassment: "Father, I said that I am actually loyal. Do you believe it?"