Final answer:
Kenneth and Mamie Phipps Clark's major contribution to the history of psychology involved research on African American children and doll preference.
Step-by-step explanation:
The major contribution of Kenneth and Mamie Phipps Clark to the history of psychology involved research on African American children and doll preference. Their research was instrumental in the Brown v. Board of Education Supreme Court desegregation case. They found that African American children were more likely to choose a White doll over a Black doll, highlighting the harmful effects of segregation and the children's unhealthy concept of themselves.