The dangerous 'Civilization Annihilator'' had launched an all-out war against the entire Milky Way.
They did not explain any reason for declaring war, nor did they create any excuse for war. They merely 'notified' the other civilizations that they wanted to destroy them and then launched an attack.
Before that, the Milky Way civilizations had also learned from the news leaked from the 'Sanctuary' circular world that the 'caterpillar fungus disease' that had ravaged the Milky Way was caused by the 'Civilization Annihilator.'
They just wanted to play the good cop and the bad cop to trick the Milky Way civilizations into putting their entire civilizations under their control.
Now that everything had been exposed, they no longer hid anything. Instead, their style changed. They had turned from benevolent hosts to cruel exterminators.