The world originally had magic. Things like angels, demons, and things from all over were in the material plane. At some point, the God's decided that it would be best for the mortal races to resolve their issues on their own. Magic came from the dragons, which were inherent to the Material plane.

So, two layers of constructs were made. One was to stop things from other planes to get into the MP. Another was an anti magic field that suppressed magic on the MP.

The players will be starting with maybe a few months or so of magic beginning to return.

With that said, I was thinking of playing it where the players had to "disarm" these constructs (just large towers basically), so magic can be used in that area (maybe 10 miles, 50, 100, I'm not yet sure). However I imagine this would make magic users difficult to play in that area. (At the same time, martial characters would thrive in the first phase, before they get disarmed).

What are your ideas on how to make disarming these part of an active quest, with danger around doing said quest, while not nullfying their class outright?

Edit: What I just came up with, and feels right, is as more of the constructs go down, the magic increases worldwide. Instead of a zone each is a battery; the fewer batteries, the stronger the anti magic effect