The magic number 21
Black Jack is undoubtedly the most popular card game in the world. Its exact origins are unkown, but 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-en-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. After 1900 American casinos offered it, but it was less popular at the beginning. Only after a few changes of the rules, Black Jack gain significantly in popularity, what is unbroken today.