Out of all the post-Nirvana American alternative bands to break into the pop mainstream Green Day were second only to Pearl Jam in terms of influence. At their core Green Day were simply punk revivalists recharging the energy of speedy catchy three-chord punk-pop songs. Though their music wasn't particularly innovative they brought the sound of late-'70s punk to a new younger generation with Dookie their 1994 major-label debut. Green Day weren't always able to sustain their success — Dookie sold over eight million while its follow-up Insomniac only sold a quarter of its predecessor — yet their influence was far-reaching because they opened the doors for a flood of American neo-punk punk metal and third wave ska revivalists