Immigrant Song" was written during Led Zeppelin's tour of Iceland, Bath and Germany in the summer of 1970. The opening date of this tour took place in Reykjavík, Iceland, which inspired Plant to write the lyrics. He explained in an interview: We weren't being pompous ... We did come from the land of the ice and snow. We were guests of the Icelandic Government on a cultural mission. We were invited to play a concert in Reykjavik and the day before we arrived all the civil servants went on strike and the gig was going to be cancelled. The university prepared a concert hall for us and it was phenomenal … 'Immigrant Song' was about that trip and it was the opening track on the album that was intended to be incredibly different. Led Zeppelin III

Six days after Led Zeppelin's appearance in Reykjavik, the band performed the song for the first time in concert during the Bath Festival.

 

Regarding the band's breakup in December 1980, it came approximately two months after the tragic death of drummer John Bonham.
The group had been preparing to commence a tour in the fall of 1980 when Bonham passed away. After a day of heavy drinking, he had gone to bed and died via asphyxiation from his own vomit. The death was ruled accidental.

Meanwhile, the group was faced with the decision of what to do without such a key piece to their lineup. The pending tour was immediately cancelled, but that didn't stop the rumors from swirling about a number of famous drummers that could potentially come on board to take over for the late musician. However, the surviving members decided that it was not right to tamper with their legacy by bringing someone else in to play drums.

In a statement, the band simply and elegantly explained their decision:
"We wish it to be known, that the loss of our dear friend and the deep respect we have for his family, together with the deep sense of undivided harmony felt by ourselves and our manager, have led us to decide that we could not continue as we were."

In the years since, Robert Plant, Jimmy Page and John Paul Jones have occasionally worked and recorded together, but reunions of all three have been few and far between. They took the stage together to perform at Live Aid in 1985, welcoming Phil Collins and the Power Station's Tony Thompson on drums. They reunited again in 1988 at the Atlantic Records 40th Anniversary concert with Bonham's son, Jason, taking his turn behind the kit.
The band's most recent reunion came in 2007 at an Ahmet Ertegun tribute show held at London's 02 Arena.

 

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