Originating from New Wave of British Heavy Metal, European branch of power metal emerged in 1980s with Germany's Helloween and Finland's Stratovarius in the 1990s, with a strong focus on melody and uplifting, positive themes. Helloween mixed fast palm muted speed metal riffs with high-pitched clean vocals and guitar. The album Keeper of the Seven Keys Part 1 was an album that made a staple for the birth of power metal. Stratovarius further developed this melodic direction by making heavy use of keyboards and neo-classical guitar solo duels which are now prevalent in almost all power metal. This genre branched and spread over Europe and into most of power metal's subgenres, incorporating further influences from classical and folk music and reinforcing the high fantasy imagery as well as sometimes developing a more emotional, romantic edge. The style has become one of the largest metal subgenres and its popularity is far from waning. The United States also has its share of European style power metal bands, an example of which is Kamelot. It should be noted that some other power metal bands put less emphasis on speed.