21 the magic number
Its exact origins are unknown, but a variety of games are likely to have developed, in which the aim was to not exceed a certain number of points. Today’s black jack is still most similar to the French game “Vingt-et-Un,” translated “21”. In the USA at the end of the 19th century it acquired the name Twenty-One, where it was played primarily in private rounds. Then after 1900 American casinos offered it, but it was less popular in the beginning. Only after a few changes in the rules die black jack gain significantly in popularity, which is unbroken today.