 This is due in part to the growing addition of bands that assimilate to common styles in NWOAHM (as defined below), yet have not differentiated greatly enough as to garner a new genre moniker.One description by longtime metal author Garry Sharpe-Young helps classify the NWOAHM as a "marriage of European-style riffing and throaty vocals" Several of the bands within the NWOAHM are credited with bringing heavy metal back into the mainstream.The new wave of American heavy metal has its origins in a group of post-grunge acts from the 1990s that brought heavy metal "back to its core brutality" and drawing not from the traditional blues formula but from thrash metal and punk.