Primal Ban

According the the Heroes of Elemental Chaos Splatbook the Primal Ban is what keeps the World safer. The Primal Ban is the manifestation of an old, deep magic that lies beyond mortal awareness or understanding. Even the spirits whose existence sustains and reinforces it have little sense of its true nature. As the Primal Spirits grew older and stronger, the Primal Ban began to take shape and grow with them. They became able to protect more and more of the world, hedging out the rampaging Primordials and mitigating godly efforts to change the world from its current shape. The Primal Ban is not absolute, nor is it impervious. The most powerful primordials and gods can resist or defy its effects with great effort. Many lesser elemental powers can do so in places where elemental influence is naturally strong in the world, or when the proper conditions lend them the strength to act. However, the surest way to circumvent the ban is to work through mortal creatures. The warding does not constrain the acts of creatures native to the natural world, so mortals who call upon divine aid or elemental energy can bring these forces into the world much more easily than gods or primordials can make their way in from outside.