For a spell, it seemed that U2 was indestructible. While 1987's \"The Joshua Tree\" cemented them as The Biggest Band Alive, the grunge movement of 1991 was picking up steam and destroying entire genres that were thought to be \"inauthentic\" (like hair metal). Lucky for U2, their music was heading in a post-ironic direction, so 1991's \"Achtung Baby\" mixed rock music with electronics that were still authentically true to U2's spirit. Some hardcore fans bemoaned the shimmering keyboards and processed drum sounds, but Bono and co. ended up finding a new audience with this aesthetic, which they continued with on 1993's deeply underrated \"Zooropa\". Despite promises to return to their rocking ways, \"Pop\" arrived like a slap in the face to their most feverish of devotees, as spelled out with its deliberately unironic title. The lead single, \"Discothèque\", was dismissed as flashy dance nonsense, and goodwill dropped off sharply because while most of \"Pop\" doesn't sound as sell-out-y as its title suggests, the damage was done. It remains one of the least popular records they've ever released. While their resulting \"PopMart\" tour made bank, the record itself sold a fraction of what the band was capable of in their heyday, which is why 2000's \"All That You Can't Leave Behind\" course-corrected and abandoned all pretenses of dance-rock entirely.