Ji Wudao had returned to the Heaven Court and killed the String Emperor and Book Deity who had been ruling the Heavenly Realm. Afterward, he reorganized the forces of the Heaven Court, aggressively killing the people who were not willing to obey him. They had to choose to either follow him or die.
In one night, the Heaven Court's master changed. Ji Wudao became the new master of the Heavenly Realm, snatching back the position of the Heavenly Emperor.
The other forces naturally received the news too. When they learned that Ji Wudao had returned and taken the Heavenly Realm, all the forces were shaken up.
Ji Wudao had already been extremely strong back then. He had once attacked the Human Realm and was known as the monstrous figure of the world, equal to Ye Futian. Now that he had returned, he had killed the String Emperor and Book Deity easily, so he had definitely gotten stronger, but it was hard to guess what level he was at.