Written during Lennon's 1969 honeymoon 'Bed-In,' Lennon's powerfully simple call-and-response anti-war refrain became an anthem of the American anti-Vietnam War movement. The first recording of the song, made in bed with minimal equipment, features Lennon's guitar and voice, accompanied by a room full of journalists, artists, and celebrities. The verses are largely improvised and contain mentions of the many onlookers. Lennon later admitted that he couldn't remember all the words.
In October 1969, the song was sung by half a million demonstrators in Washington protesting the Vietnam War. The song has since been covered by dozens of artists, including U2, Paul McCartney, Joni Mitchell, Louis Armstrong, and Elton John.