Between their massive world tours and philanthropic efforts, U2 have often kept their fans waiting many years for new music from them. That's why it seemed so unusual for them to release Zooropa on July 5, 1993, a little more than a year and a half after delivering Achtung, Baby in November 1991.

Even more startling was the music. After the anthemic post-punk of their '80s work and the moody introspection of its brilliant predecessor, Zooropa seemed to serve as a counter to the grunge of the day with electronic dance grooves, understated vocals and samples.

The group wrote much of the material while in between legs of the Zoo TV tour, which saw them embrace irony, satire and self-deprecation -- concepts not usually associated with U2 -- while taking aim at the sensory bombardment of the media. These new songs were reflective of these ideas, and they had originally planned to release it as an EP as they began their tour of Europe, but soon decided to flesh it out to a full-length.

The new direction they were taking was on display before the album was released when the first single, "Numb," arrived in June. One of the few U2 tracks that feature the Edge -- who co-produced Zooropa with Brian Eno and Flood -- on lead vocals, "Numb" is a hypnotic drone in which the Edge recites a litany of things not to do. "I feel numb / Too much is not enough," Bono sings in a falsetto on the chorus, a vocal technique also employed on the follow-up, "Lemon."

And then there was the closer, "The Wanderer," which features lead vocals by Johnny Cash, which was a head-scratcher at the time, given how the country legend had fallen out of favor with the public. But within a year, Cash would release American Recordings and begin a career renaissance and re-evaluation of his catalog that would last until his death in 2003.

Although it topped the charts worldwide, Zooropa only sold two million copies in the U.S., fewer than any U2 LP since 1981's October. To an audience weaned on Bono's vocal histrionics, the slash-and-burn attack of the Adam Clayton-Larry Mullen, Jr. rhythm section and the Edge's delayed riffs, the album felt like the work of an entirely different band, Achtung, Baby may have brought in ideas commonly found in industrial music, but its songs were still undeniably U2 underneath. Only its excellent ballads, "Stay (Faraway, So Close!)" and "The First Time," have echoes of their previous work.

And while many were turned off, especially when its follow-up, Pop, continued along those themes with diminishing returns, it's hard to see what the fuss was about now that such sounds are commonplace in indie rock. All That You Can't Leave Behind found a way to successfully combine the '80s U2 with the '90s U2 (notice how the grooves of "Lemon" worked their way into "Elevation") and the transition they made with Zooropa now doesn't seem as jarring. In that respect, Cash's cameo on "The Wanderer" is a microcosm for the entire album.

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