Medivh had a feeling that as the rules of the Endless Star Sea further corrected the imbalance between light and darkness, the restrictions the Light Covenant placed on legendary powerhouses would sooner or later be lifted.
When Medivh first started taking part in plane wars, Sixth-Rank Transcendents rarely went to ordinary battlefields. The high-ranking Transcendents who served as the pillars of their races rarely fought to the death.
When the Star Sea Myriad Races waged plane wars, they usually stopped once they had made their point and gained an advantage. They rarely fought until a nation was wiped out and its people exterminated.
After Nightmares appeared, everything changed. If you stopped once you had gained an advantage, all you got was a pile of bombs. Some hardline natives hoped to drive out invaders through suicide attacks.
Once the tactic of luring Nightmares into attacks became widespread, no one wanted strange voices near their territory, with people showing up to launch suicide attacks at any moment.
The appearance of Nightmares brought about a fundamental shift in the strategy of plane wars.
The strategy of stopping once you had gained an advantage—acquiring a colony of a certain size at minimal cost, developing it, and gradually expanding from there—no longer worked.
The more spread out your forces were, the more Other Plane colonies you had to defend, and the more trouble you faced.
Take the Gevot City-State for example. The nobles of its various city-states no longer sought to open new fronts. Instead, they focused on consolidating their existing plane colonies and unifying the plane.
Lothar City-State had suffered from having its territories spread out. When it launched an all-out war on the New Moon Plane, spies from the Duo Tuo Plane discovered its internal troop movements, and it nearly came to disaster.