In the post-World War II era, returning African-American veterans were among those who became active in pushing to regain their civil rights in the South: to be allowed to vote and participate in politics, to freely use public places, to end segregation. According to the historian David Beito of the University of Alabama, African Americans in Montgomery "nurtured the modern civil rights movement." African Americans comprised most of the customers on the city buses, but were forced to give up seats and even stand in order to make room for whites. On December 1, 1955, Rosa Parks was arrested for refusing to give up her bus seat to a white man, sparking the Montgomery bus boycott. Martin Luther King Jr., then the pastor of Dexter Avenue Baptist Church, and E.D. Nixon, a local civil rights advocate, founded the Montgomery Improvement Association to organize the boycott. In June 1956, the US District Court Judge Frank M. Johnson ruled that Montgomery's bus racial segregation was unconstitutional. After the US Supreme Court upheld the ruling in November, the city desegregated the bus system, and the boycott was ended.