A war for legitimacy!
Taiyi’s celestial court hadn't fallen apart after his death, but had instead been taken over by his old officials. In doing so, they perpetuated the fortunes of the connate demon gods and continued to represent the legitimate orthodoxy of the realm. They were also the last fortunes of the connate demon gods of the great wilderness.
Though demon gods now didn’t care about luck and providence or being recognized as the proper rulers of the world, the same didn't hold true for the human race. If they wanted to truly obtain the approval of the heavens and become principals of this realm, they would have to first wrest away the demon gods’ final wisp of fortune.
And, Lu Yun alone wouldn’t be enough for the task.
Back in his day, Taiyi had needed to convene thousands of demon gods to conquer the world of celestials and establish his court. He’d gathered the will of all connate demon gods at that time, thereby consolidating the will of all life.
Therefore, Lu Yun must also collect the strength of the human race if he wanted to seize the celestial court. He needed to occupy the world of celestials, the celestial court, and the heavenly dao with humanity’s consciousness.
“But even if the demon gods don't care about legitimacy of rule, the rise of humanity should be putting them on their guard. There's undoubtedly countless pairs of eyes fixed on the human race right now. If I do anything big, it'll probably result in their retaliation.” Lu Yun frowned slightly.
With the establishment of human dao, all life had to take shape in human form. This was far beyond the limits of demon god tolerance. If it wasn't for the cultivation method within human dao which gave them hope of becoming creators themselves, they would’ve erupted in an all out extermination of the human race a long time ago.
As strong as Lu Yun might be, he wasn't a match for all of the demon gods in the world. Even Leize had chosen to give way when faced with their collective strength.
“Thankfully there’s a Xiong Tribe that’s getting a bit antsy these days. Xiong Tribe… Xuanyuan?” Lu Yun’s frown deepened. “Xuanyuan… Xuanyuan… The Xuanyuan now shouldn't be the one that I meet in the future, right?”
He turned around and looked to the south where the Xiong Tribe was located. It was stronger than the Yan Tribe; though the Yan Tribe boasted of two human kings—the previous Shennong and Jiang Ti—the Xiong Tribe possessed three! Additionally, their chief had reached peak human king realm.
In this era, the great dao was distinct and its rules clear; cultivation was a much faster undertaking than in the future. Most importantly, the human dao had just been founded and possessed an extraordinary degree of affinity for humans. Human cultivation speed was endless times faster under the human dao than compared to the other races.
If it wasn't for Lu Yun’s primary body sitting beneath the Dao Flower to protect it from realm monsters, he would’ve descended in person to continue cultivating.
“So the Xiong tribute spirit’s already reached empyrean realm, no wonder Xuanyuan’s chafing at the current order… Well, this is a perfect opportunity. The demon gods won’t tolerate a united and harmonious human race, but if humanity splinters into constant warfare, they won't pay us as much attention then.” Lu Yun stroked his chin as a smile appeared on his face. He then left to seek out Shaodian—the previous Shennong. 
Shaodian immediately disengaged from cultivating when he sensed Lie Shan’s arrival. Under the human dao, all flaws were purified from the qi refinement method, so one could awaken from cultivation anytime they wanted to.
The previous Shennong was solidly at peak initial human king, and he was half a step away from mid-human king realm.
“Your Majesty!” Shaodian bowed when he saw his visitor.
Though Lu Yun was Shennong, he was more than chief of just the Yan Tribe. As the Flame Emperor of the human race, he was the ruler of all humanity and thus it was appropriate for Shaodian to hail him as such.
Fuxi had outlined the ways of etiquette and protocol, and the human race had adhered to those principles for thousands of years.
Lu Yun hailing himself as emperor was a kind of protocol, and so was Shaodian showing him this manner of courtesy. Though humanity was weak and fragile, they were no barbarians grubbing in the dirt, respecting only the law of the jungle. They led their lives via a code of conduct, and this was a major reason why Fuxi had chosen this race.
“There’s no need to stand on ceremony, Shaodian.” Lu Yun quickly helped him up. “How go the battles with the Xiong Tribe?”
“In response to Your Majesty, though Xuanyuan still refuses to submit, he fears your strength and doesn’t dare go on the offensive. He can only use smaller tribes as bait to continuously harass us,” Shaodian responded. “Also, the spies we’ve arranged in the Xiong Tribe have sent back word that the tribe dares defy Your Majesty because a great master has arrived in their midst.
“It’s very likely to be a chaos realm demon god, and Xuanyuan’s son Han Shuniu has taken the expert for his master.” 
“Han Shuniu?!” Lu Yun’s eyes lit up and brightened even further to hear that he’d taken a master. “Is this great master’s name Guang Chengzi?” 
“Your Majesty is wise and all-seeing. Though that person is a demon god, he calls himself a fellow daoist and practices the human qi refinement method. He’s a qi cultivator!”
Any who trained in Lu Yun’s qi refinement method were called qi cultivators, regardless of race.
“There’s nothing to worry about then, since that personage has appeared in the Xiong Tribe.” A smile crossed Lu Yun’s face. Guang Chengzi? If his guesses were correct, this would be Daoist Yuyu’s senior brother. It would seem that Hongjun’s three disciples were stretching their legs now that the connate demon gods were fading out of the world stage.
“Shaodian, choose 365 of the best Yan cultivators in the true human realm and give them to my disciple,” Lu Yun commanded solemnly.
Lu Yun then flickered over to Mount Buzhou.
“Lie Shan of the human race greets Your Majesty Wahuang!”
Though he was the Flame Emperor now, he was more humble and respectful than ever when faced with the Holy Emperors Fuxi and Wahuang. If it wasn’t for their protection in the dark ages, humanity likely would’ve gone extinct long ago.
“There’s no need for such ceremony, Flame Emperor.” Wahuang leaned comfortably against a boulder while in human form. A mischievous grin played at her lips when she looked at Lu Yun’s chest, or rather, at the little fox’s head poking out of his robes there.
Embarrassment descended when Lu Yun noticed the holy emperor’s gaze.
“So, you’ve decided to conquer the celestial court?” Wahuang asked merrily.
“No.” Lu Yun shook his head seriously. “There’s no need to, not yet. Attacking the celestial court is a move that will affect the situation as a whole. Though the demon gods have faded out of public view, they are still constantly keeping an eye on us. I’m not strong enough to conquer the celestial court yet.”
“Then what are you doing here?” Wahuang asked with surprise.
“Goumang has died and been taken over by realm monsters.”
“Mm, I know.” Dejection dimmed Wahuang’s eyes.
Goumang and Rushou had been powerful demon gods who’d once been Leize’s left and right hand demons. To think they’d die within a few short years like this!
“The Builder Tree at the heart of the Mu nation leads to the world of celestials. That’s probably the realm monsters’ true goal.” Lu Yun frowned.
“In the version of history that you know, someone smashed Mount Buzhou to pieces, and the first celestial emperor of humanity broke the Builder Tree!” Wahuang looked calmly at Lu Yun.
3. It is said that Guang Chengzi was the avatar of Dao and appeared in the human world three times: the first time as Guang Chengzi during the Yellow Emperor's reign, the second as Laozi during the Spring and Autumn period, and the third as Zhang Daoling in the Han Dynasty.
All the characters suddenly have something to do with the Yellow Emperor despite being from different tribes and factions. I think this is the author's way of saying this is when humanity truly rose up. This is the origin point.