Decline and Fall of the Earth Sphere Unified Nations
The Begining of the End
In A.Y. 158, Pendragon Aden Searlin starts the Earth Sphere Unified Nations to stabilize the Alliance and prevent a resurgence of the Mage Wars. Aden's plan is centered primarily on good-faith and economic checks and balances.
The Gudersnipe Foundation formally withdraws from the Alliance at this point, which actually does more to stabilize matters than the Pendragon's proposal. A wide-spread distrust of the Foundation existed at this time, and they became an easy scapegoat.
But the peace created by this schism was a false one at best. Nations resumed posturing and isolationism, and old rivalries crept back into perception.
The Technical End
The Earth Sphere Unified Nations functions around 230 years before fracturing completely. Economic ties maintain the false peace for the next six hundred years; but the Slayer Dragons have no more political or economic power to enforce the alliances, so any major event runs the risk of destroying Eieber's work completely.
The Actual End
For the past 600 years, the Earth Sphere Unified Nations has existed as a name and nothing else. Arindell functions as an autonomous city-state, and the Pendragons continue as defenders of good. This time is known as the Golden Age of the Slayer Dragons.
The Ninety-Nine-Years War began with unprecedented military build-ups all over the Known Worlds. Historians theorize this was a response to the growing visibility of the Gudersnipe Foundation as they build the GATE network across the entire Known Worlds.
Fighting in the Ninety-Nine-Years War
Or more accurately, lack thereof. Aside from many scattered skirmishes, very little actual fighting took place. Though they lacked the political, economic, or military power to back them, the Slayer Dragons still held an important political voice.
Acting mostly as a neutral third party, they traveled the Known Worlds mediating disputes. The Gudersnipe Foundation also helped stablize the situation by refusing to move troops over its now-complete GATE network, and instead offering its Crimson Blade mercenary division, as peace-keeping forces instead of invading armies, to maintain the tenuous balance and prevent further Mage Wars.