It only took 5000 years for cracks to appear.
The Alliance that had been formed for survival against the Fiend threat for over a million years only took 5000 to start falling apart. To be honest, the necessity suppressed tensions as any in fighting would lead to worse than death.
Such a threat made for a great motivation to cooperate even if the goals of your sect or kingdom contradicted another.
When that threat lessened and the Fiends were fairly contained for enough time, ambitions grew.
The Qi and Laws in the Celestial Fields allowed Immortals to grow like cabbages at first. Many in the current generation had struggled and comprehended for centuries to progress so when the Qi and Laws were like raindrops, they exploded forth!
It all slowed down and stabilized eventually but when that happened, various powers took stock and began to plan.
