The team's success was tragically cut short in 1967 when, during a concert appearance in Virginia, Terrell collapsed into Gaye's arms on-stage, the first evidence of a brain tumor that abruptly ended her performing career and finally killed her on March 16, 1970. Her illness and eventual loss left Gaye deeply shaken, marring the chart-topping 1968 success of "I Heard It Through the Grapevine," his biggest hit and arguably the pinnacle of the Motown sound.
At the same time, Gaye was forced to cope with a number of other personal problems, not the least of which was his crumbling marriage. He also found the material he recorded for Motown to be increasingly irrelevant in the face of the tremendous social changes sweeping the nation, and after scoring a pair of 1969 Top Ten hits with "Too Busy Thinking About My Baby" and "That's the Way Love Is," he spent the majority of 1970 in seclusion, resurfacing early the next year with the self-produced What's Going On, a landmark effort heralding a dramatic shift in both content and style that forever altered the face of black music.
A highly percussive album that incorporated jazz and classical elements to forge a remarkably sophisticated and fluid soul sound, What's Going On was a conceptual masterpiece that brought Gaye's deeply held spiritual beliefs to the fore to explore issues ranging from poverty and discrimination to the environment, drug abuse, and political corruption; chief among the record's concerns was the conflict in Vietnam, as Gaye structured the songs around the point of view of his brother Frankie, himself a soldier recently returned from combat.