What the hell were the High Lords of Terra thinking trying to stage a coup against Guilliman the Primarch of Administration?!

While fully aware that millennia has past it still amazes me that so many believe they can out-smart and out-maneuver a Primarch.

Considering Guillimen has already seen these events transpire once. It’s not really a surprise that he’d deal with it in a similar manner. He knew if he killed them outright they would more than likely become martyrs, he needed a reason. So he gave them a chance, and they blew it just as he expected.

They really should have figured out that a Primarch would be three void whales ahead.

"Authority is not given to you to deny the return of the King, Steward!" -Gandalf the White

This is what happens when you're not around godlike beings for 10 millennia. You begin to believe in your own superiority.

The Grand Master of Assassins was just fulfilling his role. He knew that his role is to remove others whom go pass the limits of their only role in the Imperial. His title and position of power was always secure. He simply fulfill his task just like any other day.

This reminds me of the War of the Beast, where Vulkan briefly returns and basically tells the High Lords of Terra, that if he would have the time for that, he would kill them all, because all their plotting, scheming and power plays is nothing less than betrayal.

Guilliman foresaw the betrayal of the High Lords because the situation is almost exactly how he lost his adoptive father (i.e. discontent Nobles, in this case, high lords, who decided to revolt while he was away on campaign).

I like to think the Emperor let out a little smile when all those traitorous heads exploded.

Guilliman: Ah how cute, I see you brought a full chapter.

"My lord Primarch, how did you comprehend such a deep conspiracy within the Imperial Bureaucracy?"

Random Imperial citizen: "We have High Lords on Terra?"

Traitor High Lords: "You will be removed from power!"

High Lords: We declare.........REBELLION!

Guilliman: Congratulations. You played yourself.

I'm not surprised he didn't kill the High lords outright. Given that his origin story with Macragge. When Konor was murdered and his murderer tried to do the same to Guilliman, Guilliman confronted him in front of the ruling body, and while the senate was damned happy to let Guilliman murder the bastard - he turned around and said 'Nope. He needs a trial. Legality must be observed'. I mean, the dude came face to face with the man who murdered his adopted dad, and his first thought was to give him a trial. Which won over the ruling class showing that, in a moment of pure emotion, he was fair and law abiding in his acts.

Officio Assasinorium kills all the other high lords

So instead of intergrating themselves into the retirement home when Guilliman politely asked them , the high lords prefer to be intergrated into the fcking dirt? They should be grateful this is Guilliman ,the Lion, the Wolf or even the Raven wont allow them to have a choice

You forgot the part when the Minotaurs decided to fight, and a certain high lord perhaps threatened to reveal their origin as Iron Warriors successors, and so they ran with their tails between their legs.