The incoming 1970s were a time of deep despair. The idealism of the '60s had been swept away by racial strife, atrocious news from Vietnam, joblessness and rampant drug casualties. Marvin Gaye, Motown's crown prince, once recalled hearing one of his own effortless love songs on the radio and feeling sick to his stomach. For an artist, the times called for a seriousness of purpose.

On the 40th anniversary of the release of 'What's Going On,' the singer's masterful testimonial to the healing possibilities of protest music, we celebrate a true pop landmark with a track-by-track breakdown of the album the great Smokey Robinson has called "the greatest album of all time."

The title track of Marvin's tour de force wasn't his at all, at least not originally. After a Four Tops show in San Francisco, where the group witnessed police harassing anti-war protesters, band member Obie Benson began working on a song about it. He enlisted the help of Motown songwriter Al Cleveland, and they made an effort to get the song to Joan Baez.