The Miami Dolphins entered the American Football League in 1966 as an expansion team. They joined the National Football League in 1970 as part of the AFL-NFL merger. They compete in the AFC East Division. In 1972 the Dolphins went 14-0 in the regular season, and went on to win Super Bowl XII. It remains the only undefeated season in NFL history. The Dolphins defended their title in 1973, winning Super Bowl XIII.