The New Wave of British Heavy Metal re-energized heavy metal in the late '70s and early '80s. By the close of the '70s, heavy metal had stagnated, with its biggest stars (Led Zeppelin, Black Sabbath) either breaking away from the genre or sinking in their own indulgence, while many of its midlevel artists were simply undistinguished, churning out bluesy hard-rock riffs. The NWOBHM kicked out all of the blues, sped up the tempo, and toughened up the sound, leaving just a mean, tough, fast, hard metallic core. It didn't make any attempts to win a wide audience -- it was pure metal, made for metal fans. Perhaps that's the reason why it's at the foundation of all modern-day metal: true metalheads either listened to this, or to bands like Metallica, which were inspired by bands like Diamond Head.