The former faction was the so called “Ancient Kingdom” which stood for freedom, equal rights and the abolition of all forms of slavery.
Its leader was Joy Boy.
The enemies of the Ancient Kingdom, the predecessors of today’s World Government, were human supremacists and promoted humans as the master race, Imu being their leader.
They fought the Ancient Kingdom and its non-human allies and eventually defeated them.
In order to remove any future threats to their dominance and supremacy, to erase the very idea that humans and evolved animals/hybrids can live equally, they destroyed all evidence that the Ancient Kingdom ever existed and spent 100 years vanquishing its influence and achievements.
We know that Zoans, not exclusively, but moreso than the other Devil Fruits, have a will on their own.
Nika’s will, being the embodiment of freedom, liberation and equality, went on to travel the world in the form of a devil fruit throughout the epochs, in a quest to find the one individual that can bring true liberation to all inhabitants of the world.
Nika does not care which species this individual is from because that was his/her stance to begin with:
Who brings liberation does not matter. It is the positive spirit, the willpower, the ability to think out of the box, to break barriers and to form genuine friendships with all kinds of people that makes one a liberator in Nika’s sense.
In this scenario, Joy Boy was the first user in history that managed to awaken Nika’s full ability.
He fought for Nika’s centuries old dream, to liberate all the races, to fight supremacy.
But eventually his effort was not enough.
Yet Joy Boy laid the groundwork for future generations that may once again try their best at achieving this admirable dream.
The Ancient Kingdom itself may have been defeated.
Meanwhile their old allies, human and evolved animal cultures alike, preserved its memory and maintained the Poneglyphs.
We can assume that Joy Boy, like Luffy, had the Voice of All Things and Future Sight.
He saw that a new warrior of liberation will be born in the far distant future.
Claiming that Joy Boy or Roger “failed” because they were not able to bring the Dawn is false.
They did their part. Without the work of the previous generations of “attempted liberators” the new generations would have nothing to build their work on.
Nobody is strong enough to achieve such a big goal all by themselves.
*Theory by solis