Twenty years ago, when the world was at war, a jeweled citadel appeared. It appeared with no explanation, seemingly out of thin air, and it appeared with inhabitants: people who could kill with a gesture, or call down a hurricane, or raise volcanos. The armies surrounding the citadel made probing strikes on it and were beaten back with contemptuous ease. Nations blamed one another for the citadel's appearance, and the eyes of the world were upon it. It wasn't until then that the first messengers left the citadel.
Its name was Chrysalis, they said, and the material it was built with was called Prism. Prism was a rare stone that had always existed, but that the nations of the world had mistaken for mere crystal, never realizing its true power. With Prism, the messengers said, anyone could taken into Chrysalis and be transformed into what its inhabitants already were: something like a human, but magnified, possessing great powers. Something they called an Eidolon.
There were only two conditions for entry into Chrysalis: the applicant who wishes to become an eidolon must offer a prism of adequate size and purity, and the applicant must not be the representative of a country that has gone to war since the offer was made (the armies that initially investigated the citadel were not considered to have broken this condition). This second condition has come to be known as the Citadel's Peace.
All eidolons are different, but as a general rule, a team of eidolons is superior to anything conventional military technology can realistically field against it. While not invincible, most eidolons possess a combination of mobility, low profile, and destructive power that is unmatched: they can pick their targets, strike without warning, and escape before any kind of effective defense can be mounted against them. The best response to an attacking eidolon, powerful enough to stop the attack and fast enough to actually get there in time, is usually... another eidolon.
Because of this military superiority, as well as the many other ways a supernatural being can be an asset to a community, twenty years after the appearance of Chrysalis the nations of the world can be divided into two categories: nations with eidolons and nations without, or Greater and Lesser Powers. Chrysalis has only existed for twenty years, and politicians are still feeling out the limits of what is considered to violate the Citadel's Peace. So far, though, these seem to be the ground rules:
Use of military forces by a nation to defend its borders does not violate the Citadel's Peace.
Selling or lending military equipment to another country does not leave the donor nation responsible for what is done with that equipment.
Eidolons themselves can freely come and go in other nations, and Chrysalis does not hold their nation of origin responsible for their actions.
What this means for the greater and lesser powers is:
Nations without eidolons rarely attack nations with them. The...