Well we already know that Zeref is related to the missing dragons, maybe this is why. "Awakening" Zeref ( still not quite sure if he was ever asleep or not ) lead to the awakening of this evil dragon who's purpose is to bring devastation to the world. The dragons couldn't allow this and so are meeting up to discuss how to stop him, maybe there's some bureaucracy involved as well.

One thing is almost certain though, someone's gonna get killed.