The Systems Commonwealth established the Quarantine Zone to keep the Magog out of Systems Commonwealth space. After the initial Magog incursion the High Guard realized that there was little chance of beating this vicious enemy back to where ever it had emerged from. Thus, the Commonwealth military decided the best they could hope for was to contain the Magog threat to those worlds they had already pillaged and made their own, and the Magog Quarantine Zone was created. The Nietzscheans felt betrayed by the creation of the Quarantine Zone since the worlds given to the Magog in the Quarantine Zone by the Treaty of Antares had been Nietzschean.
After the InsurrectionEdit
After the First Systems Commonwealth Civil War the Systems Commonwealth there was no civilization with the military strength to stop the Magog, which left them free to leave Quarantine Zone and begin attacking the defenseless Known Worlds, killing countless people in the process.
Despite the fact that they were now free to conquer the galaxy, the Magog choose not to. Unlike the Nietzscheans, the Magog have no desire to build a vast empire choosing instead to remain in the safety of the Quarantine Zone, expanding their borders only when necessary.