[Wow, no wonder his world has mana problems.]

Leylines are passageways of arcane magic that span the entire world. They flow beneath the surface, sometimes intersecting and creating places of great magical power. The way they're arranged allows magic to be distributed to every part of the land... so if someone tampers with them, it can cause problems for things that need mana to survive. [Like dragons. Though if dragons are the ones doing it, that's a great premise for a war.]

Quel'thalas, my homeland, was built on a nexus of leylines.