A series of lineup shifts followed, and at one point Hütter even left the group; however, by the release of 1972's Kraftwerk 2, he and Schneider were again working in tandem. Recorded without a live drummer, the album's rhythms relied solely on a drum machine, creating a distinctly robotic feel without precedent -- the concept of purely technological music was, at the time, utterly alien to most musicians, as well as listeners. A series of well-received live performances followed before Kraftwerk began work on their breakthrough third LP, 1973's Ralf and Florian; honing their many ambitions down to a few simple yet extraordinarily innovative concepts, their music began growing more and more revelatory -- even their clean-cut, scientific image was in direct opposition to the dominant pop fashions of the time. Kraftwerk's first album to be issued in the U.S., 1974's Autobahn was an international smash; an edited single version of the epic title track was a major hit at home and abroad, and in America the previously unknown group reached the upper rungs of the pop albums chart. Performed in large part on a Moog synthesizer, Autobahn crystallized the distinctive Kraftwerk sound while making the group's first clear overtures towards conventional pop structure and melody, establishing a permanent foothold for electronic music within the mainstream.
Kraftwerk resurfaced in 1975 with Radio-Activity, a concept album exploring the theme of radio communication; indicative of the group's new global popularity, it was released in both German and English-language editions, the latter appearing early the following year. Train travel emerged as the subject of 1977's Trans-Europe Express, which marked an increased movement towards seeming musical mechaninization; the line became even further blurred with the follow-up, 1978's aptly titled The Man Machine, a work almost completely bereft of human touches. By this time, the members of Kraftwerk even publicly portrayed themselves as automatons, an image solidified by tracks like "We Are the Robots." Having reached the peak of their influence, however, the group disappeared from view, the first of many extended absences to follow; they did not return to action prior to 1981's Computer World, a meditation on the new global dominance of technology -- a society their music long ago predicted and predated. After topping the British charts with the single "Computer Love," Kraftwerk again vanished, enjoying a five-year layoff culminating in the release of 1986's Electric Cafe. By now, however, pop music was dominated by synthesizers and drum machines, and the group's stature flagged; but for a 1991 best-of collection titled The Mix, they remained silent in the years to follow, finally releasing a new single, "Expo 2000," in late 1999. ~ Jason Ankeny, All Music Guide