[Mr. K]

Thousands of square miles is less than a 50 mile by 50 mile square.

Not big compared to the size of the country.

But put that over a grid like NYC and you would cause major problems AND cascading failures down other grids.

ONE EMP nuke would not do it, you would need several, at strategic grid points.

[T-Bone Texan]

Tens of tbousands of square miles then. A lot of square miles.