Since Earth Federation has done a very good job getting their butt kicked by Aliens and they has actively suppress those who actually wan't to help Earth. The job of defense the sacred Earth has to be done by none other than the Planet iself.
Eversince the Xeno appear in the Omniverse. Earth has been a hotspot for invasion due to the Xeno instant hatred for Humanity. With this in mind, Zen Seibertron Teikoku has tried their best slaughtering the Xeno in large number. But no matter how many they slaughter, Xeno keep popping up and have no sign of dissapearing. After million year of constantly slaughtering countless Xenos. Zen Seibertron Teikoku decide to "screw it" and opressing them instead. But the Omniverse is not a small place so no matter what they do. They can't even defend the every version off Earth from those Xeno, let alone opressing them. This result in the lost of 70% Human in the Omniverse. With the remaining 30% now under Zen Seibertron Teikoku protection
But the fear iself is lied in two pivotal Universe Earth-Primax and Earth-Mahou Shoujo. Those Universe are the Origin Universe of mankind thus destroying them mean the end off all humankind. So in those two Universe, Earth can inititate a "self-defense" system to defend iself from all kind off enemy.
Earth-Mahou Shoujo Defense System Edit
Before the year 2013, Earth Mahou Shoujo is relatively peace. However in that year, twelve Multiversal level empire has invaded Earth. To counter that threat, Earth has chosen twelve group of girl to become the Pretty Cure. After defeating those Empire and an epic showdown with an entity called Black Hole. The Pretty Cure has become goddess and thus Earth-Mahou Shoujo Defense System is no longer needed. Since they have the Pretty Cure anyway.
Earth-Primax Defense System. Edit
In Earth-Primax, the defense System has three level.
Level 1: Choukijin, group of four mechanical mythic creature that combine with each other. This is the weakest level.
Level 2: Gan Eden, an Garden that can isolated the Earth from everything else other than Cybertron.
Level 3: Earth Avatar, a group of avatar create by Earth, base on Da-Garn and his brother. Level 3 automatically activate when the number of Gundam exceed 10. This level also extend to every Universe in the Omniverse, not just Earth. It's effectively a Gundam killing machine. Level 3 is the highest level.