Do you think there is a reason Garleans can't use magic?

[RicaRuin]

Hmm yes, ascian manipualtion is also very likely. Especially with that scene at the end of 5.1. I just find it a bit odd that Emet-Selch made no mention of any and he seemed the only one. It's not as if he was inclined to be transparent about their plans, though...

There's also The Burn, that was done by Garleans, wasn't it? So perhaps it was a Garlean settlement that was destroyed by whatever is causing the same thing that causes them to not have magic.

The Burn was created by a way earlier civilisation (Allagans iirc). They used the aether saved by that Nhaama crystal in the Steppe to create a floating continent, Azys Lla. The Burn is what had been left after the land masses were set afloat.