THE DAWN OF the ’70s saw hard rock emerge as the predominant form of rock, a loud and brash style that excelled in arenas and stadiums, to which touring acts had graduated. Next to Led Zeppelin, two of the biggest groups of the time were Deep Purple and Grand Funk Railroad. After exploring pop and prog in the late ’60s, Deep Purple found their groove with their Mark II lineup in 1970, releasing In Rock, the album that broke them into the mainstream.
Meanwhile, Grand Funk Railroad became massively successful with their updated power-trio format. Despite critical denunciations and little radio airplay, the band sold millions of albums and in 1971 sold out Shea Stadium in just 72 hours, something that had taken the Beatles several weeks to do in 1965.