Before the Dawn Era there was only one system - Chaos. There were no stars or worlds in Chaos, just entropic energy, islands of matter - some as big as a moon, a multitude of energy types, and all the building blocks necessary to build worlds and gird them with life.
By accident or design, the first stars were created. They became anchors for Negative Entropy, pushing back the Chaos around them. When Creationists started creating worlds around these stars, a great war ensued. After seven millennia, this first great war of the ages, the Dawn War, ended. The defeat of the Primordials meant that Nawirrûs (everything outside of Chaos) and its worlds were here to stay as long as the Primordial Lords are kept out.