Through a combination of zealous righteousness and post-punk experimentalism, U2 became one of the most popular rock bands in the world. The Edge provided the group with a signature sound by creating sweeping sonic landscapes with his heavily processed, echoed guitars. Though the Edge's style wasn't conventional, the rhythm section of Adam Clayton and Larry Mullen Jr. played the songs as driving hard rock, giving the band a forceful, powerful edge that was designed for arena rock. And their lead singer, Bono, was a frontman who had a knack of grand gestures that played better in arenas than small clubs. It's no accident that footage of Bono parading with a white flag with "Sunday Bloody Sunday" blaring in the background became the defining moment of U2's early career -- there rarely was a band that believed so deeply in rock's potential for revolution as U2, and there rarely was a band that didn't care if they appeared foolish in the process. By 1987, the band's following had grown large enough to propel them to the level of international superstars with the release of The Joshua Tree. Unlike many of their contemporaries, U2 were able to sustain their popularity by reinventing themselves as a postmodern, self-consciously ironic dance-inflected pop/rock act, owing equally to the experimentalism of late-'70s Bowie and '90s electronic dance and techno. By performing such a successful reinvention, the band confirmed its status as one of the most popular bands in rock history, in addition to earning additional critical respect.