Extreme metal is an umbrella term that covers sub-genres.  Not comparable to a movement in music.  NWOAHM is a supposed movement that's surprisingly vague, considering that metal has allways had a following and a "movement" in America, ever since it's creation by the likes of Black Sabbath (not American).  I would argue that as home-grown metal in America (I think) started in the 70's, and the 80's, that a definable movement would be found then.  What about metal in Scandanavia?  Far more innovative in comparison to much of the American counterparts, much of which is metalcore garbage, save a few, and yet I never heard of a Europe metal movement. 
 I support the deletion of this article when it's proposed.