Quote Originally Posted by Vyrerus View Post

I've always inferred that the answer to this question is that Nidhogg basically saw Thordan VII making his plans to become God King Thordan, and so he sped up the pace of the war to try and stop that.
100% this. Midgardsormr when he came to Hydaelyn from the "Dragon Star" essentially ended up in a contract. Refuge for him and his 7 eggs and in return he guards Silvertear lake but also deals with Omega when it eventually comes knocking. Nidhogg being one of the first brood inherits this duty.

In the Dragoon 80 Quest "Gone but not forgiven" Faunehm states

"Nidhogg was without equal, even among our kind. Destined was he to guard this world from the catastrophe that befell the Dragon Star, in place of his sire. He valued strength above all else, and considered the affairs of mortals beneath his notice. Only the seven great wyrms were worthy of his attention. And among them, none but Ratatoskr truly understood him."

Nidhogg viewed mortals with loads of contempt and I assume what happened over in Meracydia with all that Eldest brother Murder could possibly have ramped that up to an extreme.

Unlike Bahamut, He didn't care about "playing nice" with humanity. However, even though his beef with the Ishgardians is a large one indeed, the prospect of a God-King terrorizing the world with one of his eyes is also quite the menace so the sooner he enacts his vengeance the better the world would be off. (At least to him)