Eventually, after long back and forth wars, The Treaty of the Mechanus was signed. In which The Planes of Mechanus and Limbo were declared the boundaries of the upper and lower planes between the Celestial beings in the Upper Planes, The Devils and Demons in the Lower Planes, and the Elemental Planes will remain held by the Primordials. The Material Plane remained a space for any who could claim it.
It was the Primordials, Celests, and Devils who crafted this treaty, fearing further breaking of the universe, for each enormous level of existence formed, there was less and less Astral Sea, from which the universe thrived off of.