Metal remained popular in the 2000s, particularly in continental Europe. By the new millennium Scandinavia had emerged as one of the areas producing innovative and successful bands, while Belgium, Holland and especially Germany were the most significant markets. Established continental metal bands that placed multiple albums in the top 20 of the German charts between 2003 and 2008, including Finnish band Children of Bodom, Norwegian act Dimmu Borgir, Germany's Blind Guardian and Sweden's HammerFall.
Metalcore, originally an American hybrid of thrash metal and hardcore punk, emerged as a commercial force in the mid-2000s. It was rooted in the crossover thrash style developed two decades earlier by bands such as Suicidal Tendencies, Dirty Rotten Imbeciles, andStormtroopers of Death and remained an underground phenomenon through the 1990s. By 2004, melodic metalcore, influenced by melodic death metal, was sufficiently popular for Killswitch Engage's The End of Heartache and Shadows Fall's The War Within to debut at number 21 and number 20, respectively, on the Billboard album chart. Bullet for My Valentine, from Wales, broke into the top 5 in both the U.S. and British charts with Scream Aim Fire (2008). Metalcore bands have received prominent slots at Ozzfest and the Download Festival.Lamb of God, with a related blend of metal styles, reached number 2 on the Billboard charts in 2009 with Wrath.
The success of these bands and others such as Trivium, who have released both metalcore and straight-ahead thrash albums, and Mastodon, who played in a progressive/sludge style, inspired claims of a metal revival in the United States, dubbed by some critics the "New Wave of American Heavy Metal". Its roots have been traced to the music of acts like Pantera, Biohazard and Machine Head, drawing on New York hardcore, thrash metal and punk, helping to inspire a move away from the Nu Metal of the early 2000s and a return to riffs and guitar solos.
The term "retro-metal" has been applied to such bands as Texas-based The Sword, California's High on Fire, Sweden's Witchcraft, and Australia's Wolfmother. The Sword's Age of Winters (2006), drew heavily on the work of Black Sabbath and Pentagram, while Witchcraft added elements of folk and psychedelic rock and Wolfmother's self-titled 2005 debut album combined elements of the sounds of Deep Purple and Led Zeppelin.