has a team ever won back to back world series
The most successful postseason team in MLB history is the New York Yankees, who have achieved three of the four instances of a franchise winning more than two World Series championships in a row (one streak each of durations 3, 4, and 5 seasons) and five of the six instances of a franchise winning the league pennant (i.e., an appearance in the World Series) more than three times in a row (three streaks of 4 seasons and two streaks of 5 seasons). The only other franchises to achieve these milestones are the Oakland Athletics, who won three consecutive championships from 1972 to 1974, and the New York Giants, who won four consecutive pennants from 1921 to 1924. The Yankees also achieved a remarkable run of appearing in 15 of the 18 World Series from 1947 to 1964.
List of Major League Baseball franchise postseason streaks