Answer by taking a quote from the following article:

Kraftwerk (German pronunciation: ['kRaftveak], "power station") is a German band formed in Dusseldorf in 1970 by Ralf Hutter and Florian Schneider. Widely considered to be innovators and pioneers of electronic music, they were among the first successful acts to popularize the genre. The group began as part of West Germany's experimental krautrock scene in the early 1970s before embracing electronic instrumentation, including synthesizers, drum machines, vocoders, and self-made instruments, in the middle of the decade. On commercially successful albums such as Autobahn (1974), Trans-Europe Express (1977), and The Man-Machine (1978), Kraftwerk developed a self-described "robot pop" style that combined electronic music with pop melodies, sparse arrangements, and repetitive rhythms, while adopting a stylized image including matching suits.

The release of Autobahn in 1974 saw Kraftwerk moving away from the sound of its first three albums. Hutter and Schneider had invested in newer technology such as the Minimoog and the EMS Synthi AKS, helping give Kraftwerk a newer, "disciplined" sound. Autobahn would also be the last album that Conny Plank would engineer. After the commercial success of Autobahn in the US, where it peaked at number 5 in the Billboard top 200, Hutter and Schneider invested in updating their studio, thus lessening their reliance on outside producers. At this time the painter and graphic artist Emil Schult became a regular collaborator, designing artwork, cowriting lyrics, and accompanying the group on tour. The year 1975 saw a turning point in Kraftwerk's live shows. With financial support from Phonogram Inc., in the US, they were able to undertake a multi-date tour to promote the Autobahn album, a tour which took them to the US, Canada and the UK for the first time. The tour also saw a new, stable, live line-up in the form of a quartet. Hutter and Schneider continued playing keyboard synthesizers such as the Minimoog and ARP Odyssey, with Schneider's use of flute diminishing. The pair also started singing live for the first time, Schneider processing his voice with a vocoder live. Wolfgang Flur and new recruit Karl Bartos performed on self-built electronic percussion instruments. Bartos also used a Deagan vibraphone on stage. The Hutter-Schneider-Bartos-Flur formation remained in place until the late 1980s and is now regarded as the classic live line-up of Kraftwerk. Emil Schult generally fulfilled the role of tour manager. After the 1975 Autobahn tour, Kraftwerk began work on a follow-up album, Radio-Activity (German title: Radio-Aktivitat). After further investment in new equipment, the Kling Klang Studio became a fully working recording studio. The group used the central theme in radio communication, which had become enhanced on their last tour of the United States. With Emil Schult working on artwork and lyrics, Kraftwerk began to compose music for the new record. Even though Radio-Activity was less commercially successful than Autobahn in the UK and United States, the album served to open up the European market for Kraftwerk, earning them a gold disc in France. Kraftwerk made videos and performed several European live dates to promote the album. With the release of Autobahn and Radio-Activity, Kraftwerk left behind avant-garde experimentation and moved towards the electronic pop tunes for which they are best known. In 1976, Kraftwerk toured in support of the Radio-Activity album. David Bowie was among the fans of the record and invited the band to support him on his Station to Station tour, an offer the group declined. Despite some innovations in touring, Kraftwerk took a break from live performances after the Radio-Activity tour of 1976. CANNOTANSWER

Where as their international breakthrough?

Autobahn would also be the last album that Conny Plank would engineer. After the commercial success of Autobahn in the US, where it peaked at number 5