As a stop on the Underground Railroad, Indianapolis had one of the largest black populations in the Northern States, until the Great Migration.[64] Led by D. C. Stephenson, the Indiana Klan became the most powerful political and social organization in Indianapolis from 1921 through 1928, controlling City Council and the Board of School Commissioners, among others. At its height, more than 40% of native-born white males in Indianapolis claimed membership in the Klan. While campaigning in the city in 1968, Robert F. Kennedy delivered one of the most lauded speeches in 20th century American history, following the assassination of civil rights leader Martin Luther King Jr.[65][66][67] As in most U.S. cities during the Civil Rights Movement, the city experienced strained race relations. A 1971 federal court decision forcing Indianapolis Public Schools to implement desegregation busing proved controversial.[68]