On December 21, 1956, buses in Montgomery, Alabama, started racially integrated service following federal court rulings ending on-board segregation. Bus boycott leaders Rev. Dr. Martin Luther King and Rev. Ralph Abernathy were among the first riders under the new scheme. Learn about the Montgomery Bus Boycott.

On December 21, 1879, Joseph Stalin was born in Gori, Georgia. In 1922, he became leader of the USSR until his death in 1953. During his time as Soviet dictator, Stalin industrialized his country, which he then led to become one of the world's two superpowers after WWII. Through his infamous purges, show trials and nationwide famines, Stalin also became responsible for millions of deaths.