The realm in which my world takes place was created by a divine being who created every aspect of it, called "Mother". Both spiritual and physical planes and all the life that exists within. Mother not only formed the planet, but also created various gargantuan structures and stellar objects, some with unknown uses. So, in a way, this being left things for the budding life on the planet to use once their civilizations advanced.
This being was destroyed by another of its kind, for now named "Warlord", who came to the realm as a conqueror, a being of great strength and power in other ways. He was never able to create in the way that Mother was, so there was a clash during the earliest times of existence where he came out victorious.
My world doesn't have a precursor race in the sense that there was once this ancient civilization that has fallen and no longer exists. Instead, the most successful of Mother's children are a race of lizardmen who advanced and evolved the fastest of all other life on the planet. They inherited the fruits of their creator and became the dominant empire in the world, eventually expanding across their continent to two others. One of these secondary continents had come to be inhabited by humans, created by Warlord, who had managed to warp some of Mother's creations into his own image. There is a lot more to get into, but the gist is that all of these early humans were left alone by Warlord and his presence on the world vanished entirely. Think tribal humans, perhaps early minor civilizations, who were enslaved by the lizardmen and completely subjugated for the benefit of their empire.
To wrap it up, these lizardmen themselves eventually collapsed as most empires do, leaving behind great cities and ruins. The humans manage to stage several successful slave rebellions and retake their continent, and this forms the early struggle for their history. The lizardmen never completely vanish, instead fracture into many smaller groups and nations. The main periods of my worlds history that I am interested in using for storytelling would be quite awhile after these events, but not so far that the history would be completely forgotten, nor that the lizardmen would gone, just greatly diminished in power and presence.
I was pretty vague about a lot of things as I could continue typing for a long long time, but thats the best TL'DR I have.